Presume / Assume

[RSDonovan]

Isn't...

"I assume you came by bus"

exactly equivalent to...

"I presume you came by bus"

?

If so, why did two words evolve meaning the same thing?

[DickieBrakelight]

presumption (as the prefix 'pre' suggests) refers to something that has yet to happen.

assumption refers to something that has already happened.

[MarkRae]

Both verbs have several meanings depending on the context in which they are used, but they don't mean entirely the same thing. E.g. you can "assume the position" but you can't "presume the position".

They coincide over the meaning of "to take to be the case or to be true; to accept without verification or proof".

This is by no means unique in English, nor even unusual. There are literally thousands of pairs of words which mean the same thing in certain contexts.

[MarkRae]

http://www.etymonline...index.php?term=assume

[Quizmonster]

Presume, from Latin praesumere, was around in English in the 1300s, so it predates assume from Latin adsumere by some two centuries. In the sense of 'take for granted' in your illustrations, they are - as Mark says above - just another example of more or less synonymous pairs which abound in our language. Like regal from Latin and and royal from French, they mean the same thing...but not always! For example, we never speak of "the regal family".

[DickieBrakelight]

Regal family? My elbow!

[Quizmonster]

Precisely, Dickie, "your elbow"...however, that was my very point! Both regal and royal mean kingly, from rex/regis and roi respectively, but they are NOT always interchangeable. Similarly, as has already been pointed out, presume and assume are not interchangeable in all circumstances.