must be true

USAGE SUMMARY

"must be true" is a correct and usable phrase in written English.
You can use it when you are making a statement that you believe to be fact. Example: The earth is round--that must be true.

✓ Grammatically correct

News & Media

Science

Encyclopedias

Human-verified examples from authoritative sources

Exact Expressions

57 human-written examples

It must be true.

The New York Times

So it must be true.

The Economist

And I think that must be true.

The New York Times

This must be true of energy supplies.

The Guardian

The silence is ear-shattering, so it must be true.

Independent

(It's all over the Internet, so it must be true).

The New Yorker

If the premises are true, the conclusion must be true.

The New York Times

Finchy's doing the voice over, so it must be true.

Independent

The advice sounds so reasonable it must be true.

The New York Times

This must be true, at least in part.

The New Yorker

So it must be true: he was past it.

The New Yorker

Expert writing Tips

Best practice

In formal logic or mathematics, use this phrase to indicate that a conclusion follows inevitably from a set of conditions.

Common error

Avoid using "must be true" when you only have a weak hunch or a personal preference; it should be reserved for situations where the evidence or logic is overwhelming.

Linguistic Context

The phrase "must be true" functions as a modal verb construction expressing epistemic necessity. It combines the modal verb "must", the linking verb "be", and the predicative adjective "true". According to Ludwig AI, it is primarily used to assert a statement that the speaker believes is a factual certainty derived from logical reasoning.

Expression frequency: Common

Frequent in

News & Media

60%

Science

25%

Encyclopedias

10%

Less common in

Social Media

3%

Reference

1%

Wiki

1%

Ludwig's WRAP-UP

In conclusion, "must be true" is a highly effective and grammatically correct phrase used to signal deductive certainty. Ludwig AI highlights its prevalence in high-authority sources like The New Yorker and The New York Times, where it often introduces a conclusion that is framed as undeniable. Whether used in a scientific theorem or a journalistic investigation, the phrase carries significant weight, implying that the speaker has evaluated the evidence and found no other possible conclusion. For writers seeking variety, alternatives like "<a href="/s/is+necessarily+true" target="_blank" rel="alternative">is necessarily true" can add a more academic tone, but the core query remains a staple of clear, assertive English prose.

More alternative expressions

Phrases that express similar concepts, ordered by semantic similarity:

has to be true

Uses the phrasal modal 'have to', which is often perceived as slightly more emphatic or informal than 'must'.

is necessarily true

Adds an adverb to emphasize that the truth is a logical requirement, common in academic and philosophical contexts.

cannot be false

Uses a negative construction to define truth by the impossibility of its opposite, a common technique in logic.

is certainly true

Explicitly states the speaker's degree of confidence using the adjective 'certainly'.

must hold true

Uses the verb 'hold' to imply that the truth persists across different conditions or over time.

is bound to be true

Suggests a sense of inevitability or destiny regarding the truth of the statement.

must be correct

Often used in the context of answers, calculations, or specific judgments rather than general concepts.

must be accurate

Shifts the focus from philosophical truth to the factual precision of data or information.

is evidently true

Implies that the truth is clear and obvious based on the available evidence.

ought to be true

Weakens the certainty slightly, expressing a strong expectation or moral necessity rather than a logical fact.

FAQs

How do I use "must be true" in a sentence?

You can use "must be true" to express a conclusion that you believe is certain based on evidence, such as: "If the data is accurate, then our hypothesis <a href="/s/must+be+true" target="_blank" rel="alternative">must be true."

What is a more formal alternative to "must be true"?

In academic or scientific writing, you might prefer to use "<a href="/s/is+necessarily+true" target="_blank" rel="alternative">is necessarily true" or "<a href="/s/is+demonstrably+true" target="_blank" rel="alternative">is demonstrably true" for greater precision.

What is the difference between "must be true" and "should be true"?

"<a href="/s/must+be+true" target="_blank" rel="alternative">must be true" indicates absolute certainty or logical necessity, whereas "<a href="/s/should+be+true" target="_blank" rel="alternative">should be true" suggests probability or expectation without 100% certainty.

Can I use "must be true" in casual conversation?

Yes, it is perfectly acceptable in casual speech, though it is often replaced by the more idiomatic "<a href="/s/has+to+be+true" target="_blank" rel="alternative">has to be true" in very informal settings.