Presume vs. Assume: What’s the Difference?

There are a lot of tricky words in English, and it’s hard to keep track of them all. The two words presume vs. assume are no different.

Both words have similar meanings, carrying with them the definition “to suppose.”

  • I suppose you are still in school.
  • I presume you are still in school.
  • I assume you are still in school.

Since their definitions are so close, many writers use them interchangeably, however, there is a subtle difference between the two that a careful writer might wish to observe.

What is the Difference Between Presume and Assume?

In today’s post, I want to go over these two words, their definitions, their functions in a sentence, and I want to show you a trick to keep them a part for future writing. After reading this, you shouldn’t ever mix up presume or assume in your writing again.

When to Use Presume

presume versus assume grammarPresume is defined as to constitute reasonable evidence for assuming; to suppose that something be the case based on probability.

  • After such a long day at work, I presume you are tired.
  • Once we saw that the plane crashed, we presumed the pilot was dead.

To presume something is to suppose based on probability or reasonable evidence. This doesn’t mean a presumption can’t be wrong, but it does mean that you have at least some faith in or reason for a presumption.

H.G. Fowler wrote that the object-clause that follows presume is what the speaker/writer really believes until he is proven incorrect.

There is also a faint sense of presumptuousness to presume, in that it is something you presuppose or count upon.

A good way to think about this is in the case of a court system. In legal proceedings, you are innocent until proven guilty. In other words, you are presumed innocent until it is proven that you are guilty. The burden of proof is on he who declares, not on he who denies.

When to Use Assume

assume or presume meaning in sentenceAssume is defined as to take for granted; suppose to be the case, without proof.

  • I assume that is your natural hair color.
  • I assume you have a job.

To assume something is to suppose without proof. In this sense, the speaker/writer feels no certainty one way or the other that his supposition is true or false.

Assume is widely used when making arguments. For instance, you may assume something your debate partner says is true just for the sake of argument.

  • Assuming what you say is true, why should I do that?
  • I assumed three things to found my theory.
  • I assume you also like pizza.

In this sense, assume is taken for granted as the basis of an argument or action, but the speaker/author still has no feeling of certainty towards their truth or falsehood.

Remember the Difference

What really separates assume vs. presume in their meanings is a degree of confidence.

With assume you have no proof for your supposition. You could say that you have Absolutely no evidence. Both absolutely and assume start with “A’s.”

With presume, you have some type of proof or probability supporting your supposition. Presume, proof, and probability all start with “P’s.”


In many simple contexts, these two words can be used interchangeably, but the careful writer may choose to observe their differences, as they do have slightly different meanings.

Presume is to suppose based on some evidence or probability.

Assume is to suppose without any proof.