Here’s a student example of an adjective followed by a ‘that’ clause.

However,

I am sure that 

the most useful English for you is American English.

PELIC Korean male level 4 writing

In the sentence above, the phrase “I am sure that” is an example of epistemic modality.

Epistemic modality is a type of linguistic modality that deals with a speaker’s evaluation or assessment of the truth of a proposition. It expresses the degree of certainty or necessity of an event or action. In this case, “I am sure that” indicates the speaker’s high degree of certainty about the proposition that follows, which is “the most useful English for you is American English.”

So, the speaker is expressing a strong belief or conviction that American English is the most useful form of English for the listener. This is not presented as an absolute fact, but rather as the speaker’s confident belief or assessment. This is a common way to express strong certainty in English.

Note, often, “that” is omitted and “I am” is contracted.  For example:

If you look inside yourself, 

I‘m sure you‘ll find something 

that you‘re really good at.

listen

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Profiling Research

In the English Grammar Profile (EGP), there are many points that are hard to differentiate and some have conflicting information.

EGP point 22 MODALITY/adjectives at A2:

I AM SURE + CLAUSE

The ‘new’ notes in the EGP are useful:

There are only examples with ‘I am sure‘ at A2 and elsewhere. ‘We are sure‘ emerges at B2. ‘We are certain‘ come in at C1. First person use is to be expected as one usually makes assertions in the first person, unless reporting.

EGP Point 2 in FOCUS at B1 is defined as:

‘IT’ + ‘BE’ ADJECTIVE + ‘THAT’ CLAUSE for focus.

*That B1 point is elaborated on its own page here.

There are three similar points in Modality and adjectives at B2.

EGP Point 135 is defined as:

‘it’ + linking verb + adjective + (‘that’) clause as a focusing device.

EGP Point 175:

HEDGING: ‘it’ + linking verb + adjective + (‘that’) clause to make an assertion less direct.

EGP Point 132:

‘be’ + ‘obvious/sure/likely/certain’ followed by a ‘that’-clause

‘sure’ in this structure is also listed at A2

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We can extend point 132, with prefixes from Pearson’s GSE 58 B1+

express various degrees of likelihood and possibility using complement clauses.
‘It’s (un)certain/(im)probable/(im)possible/(un)likely’ (+ ‘that’) + complement clause
EXAMPLE
It’s unlikely that they’ll come.
It’s possible I’m wrong.

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*Since it is unclear if these patterns are B1 or B2, we suggest falling back on the English Vocabulary Profile to give the structures a clearer difference between levels.

The following examples move beyond the linking verb ‘is’ and used vocabulary at the B2 level, so it should make a perfect example of B2 focus:

Then it became evident that it might be possible to still submit the Murphy case on the basis of the way in which he used the confessional.

listen

 

It was apparent that Captain Nemo had discovered what mankind has always sought.

listen

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iWeb division of the Ngrams for obvious|sure|likely|certain that

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1 BE SURE THAT 78151

further collocates:
1 YOU 43641
2 CAN 25148

2 I’M SURE THAT 23164 (note that the contraction is slightly more common)
3 AM SURE THAT 22640
4 ARE SURE THAT 7938
5 WAS SURE THAT 4286

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1 IS LIKELY THAT 39195

1 IT (PPH1 ) 40259
2 , 18977
3 THE 11208
4 . 11200
5 WILL (VM ) 9023

2 ‘S LIKELY THAT 14898
3 WAS LIKELY THAT 1210
4 BE LIKELY THAT 426
5 ARE LIKELY THAT 108

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1 BE CERTAIN THAT 10831
2 IS CERTAIN THAT 6006

3 AM CERTAIN THAT 4423

4 ARE CERTAIN THAT 3516
5 WAS CERTAIN THAT 2408

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1 IS OBVIOUS THAT 14586

2 ‘S OBVIOUS THAT 7046

3 WAS OBVIOUS THAT 6793
4 BE OBVIOUS THAT 2539
5 BEEN OBVIOUS THAT 300

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1 IT IS IMPORTANT THAT 74176 (This has its own B1 point)

2 IT IS POSSIBLE THAT 53215
3 IT IS CLEAR THAT 48272
4 IT IS TRUE THAT 41177
5 IT IS LIKELY THAT 38377
6 IT IS ESSENTIAL THAT 20691
7 IT IS UNLIKELY THAT 17893

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8 IT WAS CLEAR THAT 17581

9 IT IS IMPERATIVE THAT 16372
10 IT IS OBVIOUS THAT 14241
11 IT IS VITAL THAT 11381
12 IT BECAME CLEAR THAT 10788
13 IT IS EVIDENT THAT 9919
14 IT IS CRITICAL THAT 9821

15 IT SEEMS LIKELY THAT 7765

16 IT WAS OBVIOUS THAT 6686
17 IT IS INTERESTING THAT 6505
18 IT IS CRUCIAL THAT 6489
19 IT IS PROBABLE THAT 5614
20 IT BECOMES CLEAR THAT 5341

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21 IT BECAME APPARENT THAT 5296

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22 IT IS APPARENT THAT 5105
23 IT IS NECESSARY THAT 4591

24 IT SEEMS UNLIKELY THAT 4562

*It is quite clear that most BE verbs dominate these Ngrams.  Therefore we can alter our search to avoid them:

1 IT BECAME CLEAR THAT 10788
2 IT SEEMS LIKELY THAT 7765
3 IT BECOMES CLEAR THAT 5341
4 IT BECAME APPARENT THAT 5296
5 IT SEEMS UNLIKELY THAT 4562
6 IT SEEMS CLEAR THAT 3624
7 IT BECAME OBVIOUS THAT 2426
8 IT BECOMES APPARENT THAT 2379
9 IT SEEMS OBVIOUS THAT 1587
10 IT BECAME EVIDENT THAT 1578
11 IT BECOMES OBVIOUS THAT 1374
12 IT SEEMS ODD THAT 1128
13 IT SEEMS STRANGE THAT 1060
14 IT SEEMS LOGICAL THAT 842
15 IT SEEMS PROBABLE THAT 753
16 IT BECOMES EVIDENT THAT 752
17 IT SEEMS POSSIBLE THAT 725
18 IT MAKES SURE THAT 589
19 IT SEEMS INEVITABLE THAT 559
20 IT APPEARS LIKELY THAT 552
21 IT SEEMS CERTAIN THAT 519
22 IT SEEMS REASONABLE THAT 432
23 IT SEEMS PLAUSIBLE THAT 405
24 IT SEEMS IMPOSSIBLE THAT 394
25 IT SEEMS APPROPRIATE THAT 319
26 IT SEEMS APPARENT THAT 301
27 IT SEEMS EVIDENT THAT 274
28 IT SEEMED CLEAR THAT 270
29 IT SEEMS INCREDIBLE THAT 254

30 IT REMAINS TRUE THAT 250

31 IT LOOKS LIKELY THAT 233

32 IT SEEMED UNLIKELY THAT 195
33 IT SEEMED LIKELY THAT 168
34 IT SEEMED OBVIOUS THAT 157
35 IT SEEMS DOUBTFUL THAT 148

36 IT APPEARS UNLIKELY THAT 144

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