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Prepositions with nouns

Using prepositions with “assumption”

The usual fixed expression is “on the assumption that”. “Of assumption” is not a standard combination before the noun assumption.

Quick answer

Which form is correct?

Use “on the assumption that” to mean “accepting something as true for now”. “Of assumption” is generally not idiomatic before the noun assumption. You can also use “the assumption of” when assumption means taking control or responsibility.

We acted on the assumption that everyone had agreed.
The ceremony marked the assumption of office by the new president.
They continued on the assumption that the data was accurate.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
on the assumption that + clause

Expressing a belief accepted for now

Use this fixed phrase when an action depends on something believed to be true.

The team proceeded on the assumption that funding would arrive soon.
I booked the tickets on the assumption that you were free that weekend.
2
assumption of + responsibility/power

Showing that someone takes control or duty

Use “assumption of” when assumption means taking on a role, office, or responsibility.

The assumption of responsibility changed her daily workload.
The general's assumption of command happened in April.
3
assumption about + topic

Talking about beliefs regarding something

Use “about” to introduce the subject of a belief or expectation.

Their assumptions about the market proved incorrect.
We should question every assumption about customer behaviour.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
on the assumption that
She signed the contract on the assumption that payment would be immediate.
a standard expression meaning “believing something to be true”
of assumption
The phrase “of assumption” is not a normal standalone combination in modern English.
generally nonstandard before the noun assumption
assumption of
The assumption of office took place on Monday.
taking control, duty, or a position
assumption about
His assumption about the schedule was wrong.
a belief concerning a topic

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Using “of assumption” as a fixed phrase

English does not normally use “of assumption” before the noun assumption.

✕ We acted of assumption that the files were complete. ✓ We acted on the assumption that the files were complete.

Forgetting “that” after the fixed expression

The usual structure is “on the assumption that + clause”.

✕ They continued on the assumption everyone agreed. ✓ They continued on the assumption that everyone agreed.

Confusing “assumption of” with belief meanings

“Assumption of” usually refers to taking a role or responsibility, not holding a belief.

✕ Her assumption of the weather was incorrect. ✓ Her assumption about the weather was incorrect.

Quick practice

Choose the expression that matches the intended meaning.

1. We invested ___ the assumption that sales would rise.
2. The assumption ___ office will happen next week.
3. His assumption ___ the project timeline was unrealistic.

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Frequently asked questions

Is “on assumption” correct without “the”?

In formal English, the usual phrase is “on the assumption that”. Without “the”, it sounds incomplete or unnatural in most contexts.

Can I say “assumption of responsibility”?

Yes. This is a standard expression meaning that someone takes responsibility.

Is “of assumption” ever natural?

Not as a normal fixed phrase before assumption. English usually uses “on the assumption”, “assumption of”, or “assumption about” depending on meaning.

of, about, against, to or for racism? of, about, for, in or on friendship? of, about, for, on or to thing? of, about, for, to or with sex? of, about, on, to or for moon? "of access" or "with access"? "of accommodation" or "for accommodation"? "of accuracy" or "for accuracy"? "of action" or "in action"? "of actor", "with actor" or "by actor"? "of address" or "to address"? "of administration" or "in administration"?

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