Use assume when you accept something as true without proof or with little evidence. Use presume when you think something is true based on probability, context, or reasonable evidence. Merriam-Webster and Grammarly both make this distinction, while noting that the two words overlap in everyday use.

✅ I assumed the meeting was at 10 because that’s the usual time.
Here, assumed suggests a guess made without solid confirmation. Merriam-Webster describes assume this way when there is little or no evidence.

✅ Since the lights are off, I presume everyone has gone home.
Here, presume sounds more informed because there is some visible evidence. Merriam-Webster and Grammarly both say presume often implies more confidence or evidence-backed reasoning.

✅ Don’t assume she knows the deadline.
This works because the speaker warns against treating something as true without checking.

✅ We presumed the train was delayed because the platform was still crowded.
Again, presumed fits because the conclusion is based on circumstances, not pure guesswork.

The most common mistake is using assume and presume as if they always meant exactly the same thing. In casual speech, many people do blur the distinction, but in careful usage there is usually a useful difference:

Another common mistake is overthinking the distinction in ordinary conversation. Even Merriam-Webster notes that the words are close, so the contrast is real but not always dramatic.

Use this quick test:

A simple memory trick:

assume = less evidence
presume = more reason

That will help you choose the more precise word most of the time.