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.”
The word assume originated from late Middle English: from Latin assumere, from ad- ‘towards’ + sumere ‘take’. The word presume originated from late Middle English: from Old French presumer, from Latin praesumere ‘anticipate’ (in late Latin ‘take for granted’), from prae ‘before’ + sumere ‘take’
Assume as verb:
Assume is defined as to take for granted; suppose to be the case, without proof. 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?
Presume as verb:
Presume is defined as to constitute reasonable evidence for assuming; to suppose that something be the case based on probability. 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.
After such a long day at work, I presume you are tired.
Assume or presume:
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. 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.”