1. What a booster strengthens
A booster is a word or construction used to emphasise confidence in a claim: clearly, certainly, undoubtedly, undeniably, without question; It is clear/evident/undeniable that. It expresses the writer's stance rather than independently verifying truth. Clearly alone does not make weak evidence stronger.
Compare not only the markers but also what is being asserted. The figures may indicate a decline leaves the conclusion open; The figures clearly indicate a decline presents it confidently. Both are grammatical, but they serve different communicative purposes. Do not assign fixed percentages of certainty to the markers.
The records clearly show that two payments were made.
The records clearly show that two payments were made.
The conclusion drawn from the records is strengthened, not a speculation about the payments' motive.
It is undeniable that the project missed its deadline.
It is undeniable that the project missed its deadline.
The writer presents the missed deadline as indisputable; its causes may still be disputed.
2. An impersonal frame with an adjective
In It is clear that…, dummy subject it introduces an assessment of the whole message. After is, use the adjective clear, evident, obvious, or undeniable. After that comes a clause with its own subject and predicate. Its tense depends on the facts: is clear does not require a present tense in the following clause.
Compare clear and clearly: It is clear that the file is missing, but The file is clearly missing. In the first pattern, clear is a predicative adjective after is; in the second, clearly adds an assessment to the statement. That is sometimes omitted after these adjective frames without changing the meaning. Retaining it makes the clause boundary clear in a longer formal sentence; omitting it does not by itself make a sentence ungrammatical.
It + form of be + clear/evident/obvious/undeniable + (that) + subject + finite verb
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
It is evident that the figures were copied incorrectly.
It is evident that the figures were copied incorrectly.
The present assessment concerns a past action; were copied stays in the past tense.
It is clear the room is too small.
It is clear the room is too small.
This is a natural version without that; the full frame It is clear that… is also correct.
3. The adverb and its position
Clearly, certainly, undoubtedly, and undeniably can strengthen a claim without a separate It is… frame. Useful common positions are before an ordinary main verb, after the first auxiliary, or after be used as a main verb. These are guiding patterns, not a prohibition on other natural positions.
Initial Clearly,… can apply to the whole sentence. In writing, a comma helps separate this introductory comment. If a task explicitly specifies an adverb position, follow that requirement; in free writing, different placements are possible. Adverbs are not always mechanically interchangeable: clearly can refer both to clarity of expression and to the evident nature of a conclusion.
The evidence clearly shows… / The team has certainly improved… / The result is undeniably important.
The team has undoubtedly improved its response time.
The team has undoubtedly improved its response time.
Undoubtedly stands between has and improved and expresses a confident assessment of the change.
Clearly, the current room cannot accommodate everyone.
Clearly, the current room cannot accommodate everyone.
Initial clearly comments on the conclusion about the room's capacity.
4. A confident conclusion within the limits of the evidence
Strong wording is appropriate when its basis and scope are clear. The log clearly shows three interruptions describes the log. The log proves the supplier is always unreliable adds a generalisation and an evaluation that one log may not support. The second sentence can be grammatical yet unjustified in the given context.
In academic and professional writing, it is useful to separate observation from explanation: confidently report a measured result, but propose its cause more cautiously. Demonstrates, confirms, and shows also affect the strength of a conclusion. Do not replace suggests with proves merely to sound more persuasive if the data do not justify it.
The photograph clearly shows that every seat was taken.
The photograph clearly shows that every seat was taken.
The conclusion is limited to attendance at this event. It does not establish demand for every future event.
The trial clearly demonstrates a reduction in waiting time under these conditions.
The trial clearly demonstrates a reduction in waiting time under these conditions.
Under these conditions keeps the confident claim within the conditions that were tested.
5. Boosters and hedges can work together
There is no grammatical rule that a booster prohibits every hedge in the same sentence. First establish the scope of each element. In It is clear that delays are possible, the existence of a possibility is asserted confidently, not the inevitability of delays.
It is undeniable that this might possibly have some effect is syntactically possible: the writer insists that the possibility of an effect cannot be denied. Without context, it may sound overloaded or unsuitable as a direct claim about an actual effect. Editing depends on the intention: shorten it to It is clear that an effect is possible if possibility is the point, or confidently name the effect itself if it has been established.
It is clear that further delays are possible.
It is clear that further delays are possible.
The confidence concerns possibility; the sentence does not guarantee delays.
The figures clearly show a fall in costs, although the reason may be seasonal.
The figures clearly show a fall in costs, although the reason may be seasonal.
The established result and the proposed cause have different strengths within one sentence.
6. Negation changes the scope of confidence
It is clear that the device is not working confidently asserts that the device does not work; the sentence does not yet explain why. It is not clear that the device is working reports a lack of clarity about whether it works. These are different messages: absence of confirmation is not confirmation of the opposite.
Similarly, certainly not strengthens negation: The delay is certainly not acceptable. Keep the negative in the clause where it conveys the intended fact. When paraphrasing, do not turn “not proven to help” into “proven not to help”.
It is clear that the two totals do not match.
It is clear that the two totals do not match.
The mismatch is established; the negation is inside the message after that.
It is not clear that the two totals match.
It is not clear that the two totals match.
The match is uncertain. This is not a confident assertion of a mismatch.
7. Strength and tone are separate choices
Certainly and undoubtedly emphasise confidence; evident and clear present a conclusion as understandable or apparent from the circumstances; undeniable strongly restricts the room for disagreement. This is not a precise numerical scale. The choice depends on intention, genre, and the relationship with the listener.
Obviously may imply that the recipient should already know the answer. In a neutral explanation, refer to the basis and choose one appropriate booster. Insistent strings such as certainly, obviously, without question can be grammatical yet overload the text. Changing the tone does not necessarily require giving up confidence.
The signed agreement clearly states that delivery is included.
The signed agreement clearly states that delivery is included.
The confident answer rests on a document and does not belittle the recipient.
Without question, the volunteers made a valuable contribution.
Without question, the volunteers made a valuable contribution.
The strong expression is suitable for emphatic gratitude; it does not necessarily convey a measurable fact.
8. From a short claim to an argument
Before answering, identify three things: which fact is known, which claim you are prepared to defend, and what remains unknown. Then choose a frame or an adverb. One precise booster is often enough; a specific basis and a logical connection provide the rest of the persuasiveness.
You do not need to strengthen every sentence in your own paragraph. Combine a confident main claim, its basis, and an appropriate limitation or next step. When paraphrasing, preserve the given facts and intention and, where a task specifies them, the requested construction and other constraints.
It is clear that the booking process needs attention: three participants received no confirmation. A simpler form may help.
It is clear that the booking process needs attention: three participants received no confirmation. A simpler form may help.
The need for attention is strengthened, while the specific solution remains a suggestion.
The revised guide is certainly easier to navigate. Each section now has a heading, although we have not yet tested it with new readers.
The revised guide is certainly easier to navigate. Each section now has a heading, although we have not yet tested it with new readers.
The writer's evaluation is supported by a structural change, and the limits of testing are stated openly.
Common mistakes
Incorrect:It is clearly that the figures are incomplete.
Correct:It is clear that the figures are incomplete.
Before a that-clause in the It is… frame, use the adjective clear, not the adverb clearly.
Incorrect:The records undeniable show a second payment.
Correct:The records undeniably show a second payment.
To strengthen show, use the adverb undeniably; undeniable is an adjective.
Incorrect:Is evident that the room is full.
Correct:It is evident that the room is full.
In a complete English declarative sentence, this impersonal frame requires dummy subject it.
Incorrect:It is clear that has the schedule changed.
Correct:It is clear that the schedule has changed.
Here that is followed by a declarative clause with subject → verb order, not question inversion.