Five Types Involving the Subjunctive: A Corpora-based Analysis

The main goal of this paper is to provide a detailed frequency analysis of the five types it is imperative that, it is vital that, it is essential that, it is important that, and it is necessary that within the British National Corpus (100 million, British, 1980s-1993), the Corpus of Contemporary American English (1.0 billion, US, 1990-2019), the Corpus of Historical American English (400 million, US, 1810s-2000s), and the Hansard Corpus (1.6 billion, British Parliament). In this paper, we have examined the frequency of the five types and collected the data. A major point to note is that it is important that was the most preferred by British people, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. The BNC clearly shows, on the other hand, that it is important that was the most commonly used one in the spoken genre, magazine genre, newspaper genre, and academic genre. A further point to note is that it is important that was the most preferred by Americans, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. The COCA clearly indicates that it is important that was the most widely used one in the blog genre, web genre, spoken genre, fiction genre, magazine genre, newspaper genre, and academic genre. The reason why it is important that was the most preferred by Americans and British people in the academic genre may be that a moderate obligation is suitable for conveying factual information. With respect to the COHA, it is worth noting that it is necessary that was the most preferred by Americans from 1810 to 2000, followed by it is important that, it is essential that, it is imperative that, and it is vital that. As for the HC, it is important that was the most preferred by British politicians, followed by it is essential that, it is vital that, it is necessary that, and it is imperative that. It is worth noting that Americans and British politicians show the similar pattern in the ranking of the five types in that Americans did not prefer a strong statement or the strongest statement, whereas British politicians did not prefer the strongest statement.


Introduction
The main goal of this paper is to provide a detailed frequency analysis of the five types it is imperative that, it is vital that, it is essential that, it is important that, and it is necessary that within the British National Corpus, the Corpus of Contemporary American English, the Corpus of Historical American English, and the Hansard Corpus. We use the subjunctive after these five types: (1) It's essential/imperative/important/necessary/vital that something happen.
(2) It is essential that everyone be at work by 9:00 tomorrow morning. No exceptions.
(3) It is imperative that government do something about health care. (Murphy, 2016, p. 64) As alluded to in (1), (2), and (3), we use the subjunctive after the five types it is imperative that, it is vital that, it is essential that, it is important that, and it is necessary that. In this paper, we will answer the following main questions: Which type was the most frequently used one in the BNC? Which type was the most widely used one in the COCA? What does the frequency of the five types in the BNC, COCA, COHA, and HC indicate? What are the main difference between results from the BNC and those from the COCA? What are the key difference between results from the COHA and those from the HC? This paper is organized as follows. In section 2.1, we argue that it is important that was the most preferred by British people, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. The BNC clearly indicates that it is important that was the most commonly used one in the spoken genre, magazine genre, newspaper genre, and academic genre. It is worth noting that types with the strongest one or the weakest one in their meaning such as it is imperative that and it is necessary that were not preferred by British people in the spoken genre. In section 2.2, we contend that it is important that was the most preferred by Americans, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. The COCA clearly shows that it is important that was the most widely used one in the blog genre, web genre, spoken genre, fiction genre, magazine genre, newspaper genre, and academic genre. A major point to note is that it is important that is the most widely used one in the shared on-line journal, whereas it is necessary that is the most undesired one in it. Additionally, we argue that the reason why it is important that was the most preferred by Americans and British people in the academic genre may be that a moderate obligation is suitable for conveying factual information. In section 2.3, we maintain that it is necessary that was the most preferred by Americans from 1810 to 2000, followed by it is important that, it is essential that, it is imperative that, and it is vital that, in that order. In section 2.4, we examine the frequency of the five types in the Hansard Corpus . We contend that it is important that was the most preferred by British politicians, followed by it is essential that, it is vital that, it is necessary that, and it is imperative that. Also, we argue that the reason why it is imperative that was the most undesired one may be that British politicians did not prefer the strongest obligation (the strongest statement) among the five types. www.scholink.org/ojs/index.php/selt Studies in English Language Teaching Vol. 8, No. 4, 2020 50 Published by SCHOLINK INC.

The Genre Frequency of the Five Types in the BNC
In what follows, we examine the frequency of the five types in the BNC (the 1980s-1993). Table 1 shows the use and frequency of the five types in the BNC: An important question to be asked is "which type was the one most frequently used among the five types in the BNC?" Table 1 clearly indicates that the type it is important that was the most widely used one in the UK. It is important that has the highest frequency (648 tokens) and the highest proportion (54.04%) among the five types, which indicates that it was the most preferred by British people. On the other hand, the type it is necessary that has the lowest frequency (42 tokens) and the lowest proportion (3.50%), which suggests that it was the most undesired one in the UK. Table 1 clearly suggests that it is important that was the most preferred by British people, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. When it comes to the meaning of the five types, the type it is imperative that is the strongest one, followed by it is vital that, it is essential that, it is important that, and it is necessary, as indicated in (4): (4) It is imperative that > It is vital that > It is essential that > It is important that > It is necessary that What is interesting is that types with the strongest one and the weakest one in their meaning was not preferred by British people, as illustrated in (5). (5) shows British people's preference towards the five types: (5) It is important that > It is essential that > It is vital that > It is imperative that > It is necessary that As indicated in (5), it is imperative that with the strongest one in its meaning ranks fourth and it is vital that with a strong one in its meaning ranks third. On the other hand, it is necessary that with the weakest one in its meaning ranks fifth. This in turn suggests that types with the strongest one or the weakest one in their meaning was not preferred by British people. Note, however, that the types it is important that and it is essential that with a moderate one in their meaning were widely used in the UK.
Now attention is paid to the spoken genre in the BNC. A question which naturally arises is "which type was the most widely used one in the spoken genre?" Table 1 clearly shows that it is important that was the most commonly used one in the spoken genre (23 tokens). More specifically, the type it is important that was the most frequently used one in the BNC, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. Noteworthy is that the frequency of the spoken genre and the overall frequency of the five types show the same pattern in the ranking of the five types. This implies that types with the strongest one and the weakest one in their meaning were not preferred by British people in the spoken genre. More specifically, types with the strongest one or the weakest one in their meaning such as it is imperative that and it is necessary that were not preferred by British people. It is worth noting, however, that types with a moderate one in their meaning were preferred by British people in the spoken genre. Why did this happen? We wish to argue that to use it is imperative that with the strongest one in its meaning may be a burden to the hearer, which leads to the infrequency of it is imperative that. Likewise, to use it is necessary that with the weakest one in its meaning may not accomplish the speaker's intention in his or her conversation since the type it is necessary that is weak. However, it is important that with a moderate one in its meaning may be neither a burden nor obligation to the hearer. This may be why the type it is important that was the most frequently used one in the spoken genre.
Now an immediate question to be asked is "which type was the most widely used one in the fiction genre?" Table 1 clearly indicates that it is vital that was the most frequently used one in the fiction genre. More specifically, it is vital that was the most preferred by British people in the fiction genre, followed by it is important that, it is essential that, and it is imperative that and it is necessary that, in that order. Again, types with the strongest one and the weakest one in their meaning were not preferred by British people in the fiction genre. However, it is vital that with a strong one in its meaning was the most preferred by British people? Why was it the most preferred by British people? We wish to argue that authors encourage readers to read a book with excitement and thus it is vital that with a strong one in its meaning is suitable for exciting readers. Note, however, that it is necessary that with the weakest one in their meaning may not excite readers since it is the weakest one among the five types. Now a question which arises is "which type was the most commonly used one in the magazine genre?" Table 1 clearly shows that it is important that was the most widely used one in the magazine genre.
More specifically, it is important that has the highest frequency (23 tokens) and the highest proportion (37.70%). As alluded to in Table 1, it is important that was the most preferred by British people in the magazine genre, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. Why were the types it is important that and it is essential that widely used by British people in the magazine genre? We wish to argue that it is important that and it is essential that are suitable for conveying articles, information, and ads in that they have far-reaching effects since it is neither the strongest one nor the weakest one. Note that it is imperative that and it is necessary that were not preferred by British people. It is imperative is too strong to use it in the magazine and it is necessary that is too weak to use it. Now an important question to be asked is "which type was the most frequently used one in the newspaper genre?" Table 1 indicates that it is important that was the most widely used one in the newspaper genre. More specifically, it is important that obtains the highest frequency (32 tokens) and the highest proportion (35.55%) among the five types. As illustrated in Table 1, it is important that was the most preferred by British people in the newspaper genre, followed by it is vital that, it is essential that, it is imperative that, and it is necessary that, in that order. Why were the types it is important that and it is vital that commonly used by British journalists in the newspaper genre? We wish to argue that just in the case of the magazine genre, it is important that and it is vital that are neither the strongest one nor the weakest one in their meaning. Newspapers are mainly used to convey news, articles, information, and ads and thus they are supposed to be fair. This may be why it is important that and it is vital that are wildly used by British journalists. Note, however, that it is imperative that is too strong to use it in the newspaper and it is necessary that is too weak to use it. Now attention to paid to the academic genre. A question to be asked is "which type was the most frequently used one in the academic genre?" Table 1 clearly shows that it is important that was the most commonly used one in the academic genre. The type it is important that obtains the highest frequency (133 tokens) and the highest proportion among the five types. As indicated in Table 1, it is important that was the most preferred by British people in the academic genre, followed by it is essential that, it is vital that, it is necessary that, and it is imperative that, in that order. Why were the types it is important that and it is essential that widely used by British people in the academic genre?
We intend to argue that the academic genre is characterized as a knowledge database and that it is important that and it is essential that are mainly used to convey factual information since they are neither the strongest statement nor the weakest statement. Simply put, it is important that and it is essential that are suitable for conveying factual information since they are impartial with respect to their meaning.

The Genre Frequency of the COCA
In what follows, we examine the frequency of the five types in the COCA (1990-2019) and compare results from the COCA and those from the BNC in order to observe the national variation. Table 2 shows the use and frequency of the five types in the COCA: Now an important question to be asked is "which type was the most frequently used one among five types in America?" Table 2 clearly indicates that the type it is important that was the most widely used one in America. More specifically, it is important that obtains the highest frequency (2004 tokens) and the highest proportion (49.25%). On the other hand, it is necessary that obtains the lowest frequency (224 tokens) and the lowest proportion (5.50%). As alluded to in Table 2, it is important that was the most preferred by Americans, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. Note that it is important that was the most preferred by British people, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order.
The COCA and BNC have two things in common. That is to say, it is important that has the highest frequency and it is necessary that has the lowest frequency. This in turn suggests that it is important that was the most preferred by Americans and British people, whereas it is necessary that was the most undesired one in America and the UK. It is worth noting, however, that it is imperative that ranks second in the COCA, whereas it is essential that ranks second in the BNC. In addition, it must be noted that it is essential that ranks third in the COCA, whereas it is vital that ranks third in the BNC.
Noteworthy is that Americans were fond of using it is imperative that with the strongest one in its meaning after it is important that, whereas British people were fond of using it is essential that with a moderate one in its meaning after it is important that. Now let us turn our attention to the blog genre. The blog genre was first introduced in the COCA in 2020. Which type is the most commonly used one in the blog genre? Table 2 clearly indicates that it is important that is the most widely used one in the blog genre. More specifically, it is important that has the highest frequency (348 tokens) and the highest proportion (54.37%) in the blog genre. As indicated in Table 2, it is important that is the most preferred by Americans in the blog genre, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. A blog is defined as "a website where an individual person, or people representing an organization, write regularly about recent events or topics that interest them, usually with photos and links to other websites that they find interesting" (Oxford Learner's Dictionaries). It is noteworthy that it is important that is the most widely used one in the shared on-line journal, whereas it is necessary that is the most undesired one in it. Just as in the case of the ranking of the overall frequency, it is imperative that ranks second in the blog genre. This in turn indicates that Americans are fond of using it is imperative that with the strongest one in its meaning in the blog genre. Now attention is paid to the web genre, which was first introduced in the COCA in 2020. A question to be asked is "which type is the most widely used one in the web genre?" Table 2 clearly shows that it is important that is the most frequently used one in the web genre. More specifically, it is important that has the highest frequency (363 tokens) and the highest proportion (51.85%), whereas it is vital that has the lowest frequency (51 tokens) and the lowest proportion (7.28%). As illustrated in Table 2, it is important that is the most preferred by Americans in the web genre, followed by it is essential that, it is imperative that, it is necessary that, and it is vital that, in that order. Let us consider the TV-movie genre, which was first introduced in the COCA in 2020. An immediate question to be asked is "which type is the most commonly used one in the TV-movie genre?" Table 2 indicates that it is imperative that is the most widely used one in the TV-movie genre. More specifically, it is imperative that has the highest frequency (76 tokens) and the highest proportion (44.44%), whereas it is necessary that has the lowest frequency (13 tokens) and the lowest proportion (7.60%). As illustrated in Table 2, it is imperative that is the most preferred by Americans, followed by it is important that, it is vital that, it is essential that, and it is necessary that, in that order. The reason why it is imperative that is the most frequently used one in the TV-movie genre may be that it can give an impact to TV audience or movie viewers. Note that it is imperative that is the strongest one in its meaning among the five types. Additionally, it is significant to note that it is important that ranks second and that it is necessary that ranks fifth. The reason why it is necessary that is the most undesired one among the five types is that it is the weakest one in its meaning and thus to use it is necessary that cannot give an impact to TV audience or movie viewers. Now let us consider the spoken genre. Which type was the most frequently used one among the five types? Table 2 clearly shows that it is important that was the most commonly used one in the spoken genre. As indicated in Table 2, it is important that was the most widely used one in America, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. The COCA and BNC show the similar pattern in the frequency of the spoken genre. As observed earlier, it is important that was the most frequently used one in the BNC, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. This suggests that it is important that was the most preferred by Americans and British people and that it is necessary that was the most undesired one in America and the UK. The reason why it is important that was the most preferred by Americans and British people may be that it carries a moderate one in its meaning and thus to use it is important that is neither a burden nor obligation to the hearer. The reason why it is necessary that was the most undesired one in America and the UK may be that it is necessary that is so weak in its meaning, eventually leading to the infrequency of it is necessary that. Now let us observe the fiction genre. An important question to be asked is "which type was the most widely used one in America?" Table 2 clearly indicates that it is important that was the most commonly used one in the fiction genre. More specifically, it is important that obtains the highest frequency (25 tokens) and the highest proportion (37.87%), whereas it is vital that obtains the lowest frequency (5 tokens) and the lowest proportion (7.57%). As illustrated in Table 2, it is important that was the most preferred by Americans in the fiction genre, followed by it is imperative that, it is necessary that, it is essential that, and it is vital that, in that order. Note that it is vital that was the most preferred by British people in the fiction genre, followed by it is important that, it is essential that, and it is imperative that and it is necessary that, in that order. We take this as indicating that British people were fond of using it is vital that with a strong one in its meaning in the fiction genre, whereas Americans were fond of using it is important that with a moderate one in its meaning. It must be noted, however, that it is vital that was the most undesired one in America, whereas it is necessary that was the most undesired one in the UK. Now let us turn our attention to the magazine genre. Which type was the most frequently used one in the magazine genre? Table 2 clearly shows that it is important that was the most commonly used one in the magazine genre. More specifically, it is important that has the highest frequency (157 tokens) and the highest proportion (47%), whereas it is necessary that has the lowest frequency (6 tokens) and the lowest proportion (1.79%). As alluded to in Table 2, it is important that was the most preferred by Americans in the magazine genre, followed by it is imperative that, it is essential that, it is vital that, and it is necessary, in that order. As observed earlier, it is important that was the most preferred by British people in the magazine genre, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. The COCA and BNC have two things in common. That is to say, it is important that was the most preferred by Americans and British people and it is necessary that was the most undesired one in America and the UK. The reason why it is important that was the most preferred by American and British writers may be that it carries a moderate one in its meaning and a moderate obligation is suitable for conveying articles, information, and ads. On the other hand, the reason why it is necessary that was the most undesired one in America and the UK may be that it is the weakest one in the five types and thus the weakest obligation is not suitable for conveying articles, information, and ads. Additionally, it is significant to note that it is imperative that was the most widely used one in America after it is important that, whereas it is essential that was the most commonly used one in the UK after it is important that. This in turn suggests that Americans were fond of using it is imperative with the strongest one in its meaning in the magazine genre, whereas British people were fond of using it is essential that with a moderate one in its meaning. Now let us consider the newspaper genre. Which type was the most frequently used one in the newspaper genre? Table 2 clearly indicates that it is important that was the most widely used one in the newspaper genre in America. Specifically, it is important that has the highest frequency (119 tokens) and the highest proportion (47.79%) among the five types, whereas it is necessary that has the lowest frequency (4 tokens) and the lowest proportion (1.6%). As illustrated in same pattern in the ranking of the five types. That is to say, it is important that was the most preferred by American writers and journalists, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. Now let us observe the frequency of the academic genre. A question which arises is "which type was the most commonly used one in the academic genre?" Table 2 clearly shows that it is important that was the most frequently used one in the academic genre. More specifically, it is important that obtains the highest frequency (793 tokens) and the highest proportion (46.59%), whereas it is necessary that obtains the lowest frequency (103 tokens) and the lowest proportion (6.05%). As indicated in Table 2, it is important that was the most preferred by Americans, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. Note that it is important that was the most preferred by British people in the academic genre, followed by it is essential that, it is vital that, it is necessary that, and it is imperative that, in that order. The COCA and BNC have one thing in common.
That is, it is important that was the most preferred by Americans and British people. The reason why it is important that was the most preferred by Americans and British people may be that a moderate obligation is suitable for conveying factual information. It must be noted that it is imperative that was the most preferred by Americans after it is important that, whereas it is essential that was the most preferred by British people after it is important that. This in turn suggests that Americans liked using a strong obligation in the academic genre, whereas British people liked using a moderate obligation. A further point to note is that it is necessary that was the most undesired one in America, whereas it is imperative that was the most undesired one in the UK. This indicates that Americans did not prefer the weakest obligation in the academic genre among the five types, whereas British people did not prefer a strong obligation. Finally, it is worth pointing out that the magazine genre, newspaper genre, and academic genre show the same pattern in the ranking of the five types. That is to say, it is important that was the most preferred by Americans, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that.

The Frequency of the Five Types in the COHA
In what follows, we examine the frequency of the five types in the COHA . Table 3 shows the frequency of it is necessary that, it is important that, it is essential that, it is imperative that, and it is vital that: A question which naturally arises is "which type was the most frequently used one for one hundred and ninety years (1810-2000)?" Table 3 clearly indicates that it is necessary that was the most widely used one for one hundred and ninety years. More specifically, it is necessary that has the highest frequency (496 tokens) and the highest proportion (38.39%), whereas it is vital that has the lowest frequency (41 tokens) and the lowest proportion (3.17%). As alluded to in Table 3, it is necessary that was the most preferred by Americans from 1810 to 2000, followed by it is important that, it is essential that, it is imperative that, and it is vital that, in that order. Most interestingly, the ranking of the five types in the COHA is different from that of the five types in the BNC and COCA. As observed earlier, it is important that was the most preferred by British people, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. On the other hand, it is important that was the most preferred by Americans from 1990 to 2019, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. A major characteristic of the frequency of the five types in the COHA is that it is necessary that with the weakest obligation was the most preferred one from 1810 to 2000, which is different from the result of the BNC and that of the COCA. When it comes to the frequency of the five types in the COCA and BNC, it is important that with a moderate obligation was the most preferred by Americans and British people. A further point to note is that it is vital that with a strong obligation was the most undesired one in America from 1810 to 2000, which is different from the result of the COCA and that of the BNC. In the COCA and BNC, it is necessary that with the weakest obligation was the most undesired one among the five types. Additionally, it is worth noting that Americans did not prefer it is imperative that with the strongest obligation and it is vital that with a strong obligation, which in turn suggests that Americans avoided strong statements from 1810 to 2000. On the other hand, British people avoided the weakest statement among the five types. Table 3, the frequency of it is necessary that continued to increase to 33 tokens from 1810 to 1830. After this period, there were slight fluctuations in the frequency of it is necessary that from 1840 to 2000. A major point to note is that the frequency of it is necessary that reached a peak in the 1920s (50 tokens). This indicates that the type it is necessary that was the most preferred by Americans in the 1920s. In addition, it is necessary that was the most preferred by Americans among the five types in the 1920s. After this period, there were slight fluctuations in the figure of it is necessary that and its figure continued to decrease from 1970 to 2000.

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As can be seen from Table 3, the figure of it is important that continued to increase to 19 tokens from 1810 to 1850. After this period, there were slight fluctuations in the frequency of it is important that from 1860 to 2000. It is significant to note that it is important that reached a peak in the 1990s (36 tokens). It is important that was the most preferred by Americans in the 1990s. In addition, it was the most preferred by Americans among the five types in the 1990s. A further point to note is that it is important that was the most preferred by Americans among the five types from 1930 to 2000.
As illustrated in Table 3, the figure of it is essential that continued to increase to 8 tokens from 1810 to 1830. There were slight fluctuations in the figure of it is essential that from 1840 to 2000. A major point to note is that it is essential that reached a peak in the 1960s. It was the most preferred by Americans in the 1960s. It must be noted, however, that it is essential that ranked second among the five types in the 1960s. Table 3, the number of the token of it is imperative was 0 from 1810 to 1830. After this period, there was an increase in the figure of it is imperative that. A major point to note is that it is imperative that reached a peak (18 tokens) in the 1940s. This indicates that it is imperative that was the most preferred by Americans in the 1940s. It should be noted, however, that it is imperative that ranked fourth among the five types in the 1940s.

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As can be seen from Table 3, the number of the token of it is vital that was 0 from 1810 to 1890 and there was an increase in the figure of it is imperative that from 1900 to 1930. After this period, there were slight fluctuations in the frequency of it is vital that. A point to note is that it is vital that reached a peak (7 tokens) in the 1960s and the 1970s. This suggests that it is vital that was the most preferred by Americans in the 1960s and the 1970s. It must be noted, however, that it is vital that ranked fifth among the five types in the 1960s and the 1970s. This in turn suggests that it is vital that was the most undesired one among the five types in America.

The Frequency of the Five Types in the Hansard Corpus
In what follows, we examine the frequency of the five types in the Hansard Corpus . The Hansard Corpus contains nearly every speech given in the British parliament from 1803 to 2005. Table   4 shows the frequency of it is important that, it is essential that, it is vital that, it is necessary that, and it is imperative that: and the highest proportion (54.04%), whereas it is imperative that obtains the lowest frequency (1,880 tokens) and the lowest proportion (2.53%). As alluded to in Table 4, it is important that was the most preferred by British politicians, followed by it is essential that, it is vital that, it is necessary that, and it is imperative that, in that order. That it is important that was the most preferred by British politicians indicates that they liked using a moderate obligation among the five types. Also, they preferred it is essential that with a moderate obligation. This in turn indicates that they were keen on using a moderate statement in the British parliament. A point to note is that it is imperative that was the most undesired one in the British parliament among the five types. Why did this happen? We wish to argue www.scholink.org/ojs/index.php/selt Studies in English Language Teaching Vol. 8, No. 4, 2020 60 Published by SCHOLINK INC.
that the reason why it is imperative that was the most undesired one may be that British politicians did not prefer the strongest obligation (the strongest statement) among the five types. This may reflect a spirit of democracy in that democracy is an agreement and calls for cooperation and compromise. The strongest statement (obligation) may only interfere with an agreement or compromise and thus a moderate statement is the preferred one among the five types. On the other hand, it is necessary that was the most preferred by Americans from1810 to 2000, followed by it is important that, it is essential that, it is imperative that, and it is vital that, in that order. This suggests that a strong statement was the most undesired one in America. Americans and British politicians show the similar pattern in the ranking of the five types in that Americans did not prefer a strong statement or the strongest statement, whereas British politicians did not prefer the strongest statement. Note, however, that it is necessary that with the weakest obligation was the most preferred by Americans from 1810 to 2000, whereas it is important that with a moderate obligation was the most preferred by British politicians from 1800 to 2000. This in turn indicates that Americans were keen on using the weakest statement from 1810 to 2000, whereas British politicians were keen on using a moderate statement from 1800 to 2000. Table 4, the figure of it is important that continued to increase to 11,331 tokens from 1830 to 1990. That is to say, there was a dramatic increase in the frequency of it is important that from 1830 to 1990. A major point to note is that it is important that reached a peak in 1990, which indicates that it is important that was the most preferred one in the British parliament in 1990. In addition, it is important that was the most preferred by British politicians in the British parliament among the five types from 1950 to 2000. It must be noted that it is important that was the most undesired one in 1820.

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In 1820, the number of the token of it is important that was 0, which indicates that it was the most undesired one in 1820.
As can be seen from Table 4, the frequency of it is essential that continued to increase for one hundred years from 1840 to 1940. That is to say, there was a dramatic rise in the frequency of it is essential that 1840 to 1940. It is noteworthy that it is essential that reached a peak in 1990, which implies that it was the most preferred one in the British parliament. In addition, it is important that ranked first and it is essential that ranked second among the five types in 1990. It is worth noting that it is essential that was the most preferred by British politicians in the British parliament among the five types from 1900 to 1940. This indicates that a moderate statement was the most preferred one in the British parliament from 1900 to 1940. It should be noted, however, that in 1820, it is essential that had the lowest frequency (0 token).
As illustrated in Table 4, with respect to it is vital that, it is interesting to note that there was no frequency (0 token) from 1800 to 1880. We do not know why this happened in this period (1800-1880).
However, after this period, the frequency of it is vital that continued to increase to 2,092 tokens from 1890 to 1990 (1 token-2,093 tokens). Simply put, there was a dramatic increase in the figure of it is vital that from 1890 to 1990. Noteworthy is that it is vital that was the most preferred by British politicians in the British parliament in 1990. That is to say, it is vital that reached a peak in 1990. However, it is vital that ranked third among the five types in 1990. Table 4, there were slight fluctuations in the figure of it is necessary that from 1800 to 2000. A major point to note is that it is necessary that was the most undesired one in 1810. After this period, the frequency of it is necessary that continued to increase from 1810 to 1860 (11 tokens-172 tokens). After this period, there was slight fluctuations in the frequency of it is necessary that from 1860 to 2000. It is significant to note that it is necessary that reached a peak in 1910. This indicates that it is necessary that was the most preferred by British politicians in the British parliament. In addition, it is necessary that ranked first among the five types in 1910, which implies that it was the most preferred by British politicians in the British parliament among the five types.

As indicated in
It is worth pointing out that as can be seen from Table 4, it is imperative that had no frequency (0 token) from 1800 to 1840. After this period, there was a gradual rise in the frequency of it is imperative that from 1880 to 1990. A major point to note is that it is imperative that reached a peak in 1990, which in turn suggests that it was the most preferred by British politicians in the British parliament in 1990. It must be noted, however, that it is imperative that ranked fourth among the five types in 1990. We thus conclude that it is imperative that was the most preferred by British politicians in 1990, but it was the most undesired one in British parliament in 1800, 1810, 1820, 1830, 1840, and 1870 (0 token).

Conclusion
To sum up, we have provided a detailed frequency analysis of the five types it is imperative that, it is vital that, it is essential that, it is important that, and it is necessary that within the British National Corpus, the Corpus of Contemporary American English, the Corpus of Historical American English, and the Hansard Corpus. In section 2.1, we have argued that it is important that was the most preferred by British people, followed by it is essential that, it is vital that, it is imperative that, and it is necessary that, in that order. The BNC clearly shows that it is important that was the most commonly used one in the spoken genre, magazine genre, newspaper genre, and academic genre in the BNC. It is worth pointing out that types with the strongest one or the weakest one in their meaning such as it is imperative that and it is necessary that were not preferred by British people in the spoken genre. We have maintained that the academic genre is characterized as a knowledge database and that it is important that and it is essential that are mainly used to convey factual information since they are neither the strongest statement nor the weakest statement. In section 2.2, we have contended that it is important that was the most preferred by Americans, followed by it is imperative that, it is essential that, it is vital that, and it is necessary that, in that order. The COCA clearly indicates that it is important that is the most widely used one in the blog genre, web genre, spoken genre, fiction genre, magazine genre, newspaper genre, and academic genre. A point to note is that it is important that is the most widely used one in the shared on-line journal, whereas it is necessary that is the most undesired one in it. Additionally, we have argued that the reason why it is important that was the most preferred by Americans and British people in the academic genre may be that a moderate obligation is suitable for conveying factual information. In section 2.3, we have maintained that it is necessary that was the most preferred by Americans from 1810 to 2000, followed by it is important that, it is essential that, it is imperative that, and it is vital that, in that order. In section 2.4, we have examined the frequency of the five types in the Hansard Corpus . We have contended that it is important that was the most preferred by British politicians, followed by it is essential that, it is vital that, it is necessary that, and it is imperative that. Finally, we have argued that Americans and British politicians show the similar pattern in the ranking of the five types in that Americans did not prefer a strong statement or the strongest statement, whereas British politicians did not prefer the strongest statement.