The words ‘assume’ and ‘presume’ are so close in their meaning that many dictionaries treat them as synonyms. Both ‘assume’ and ‘presume’ indicate in some way or the other ‘to take or suppose something to be true or possible without any conscious effort at questioning the validity of this supposition’.
But actually there is a subtle difference in their meanings and usage. When you ‘assume’ something to be one way or the other, it is more of a proposition based on hypothetical grounds; for example, as used in mathematics: Assume A=B, or whatever.
Thus, ‘assume’ refers to taking something to be true, or otherwise, just like that, without any rhyme or reason, maybe simply for argument sake. The person is very much aware that what he has taken as true, or otherwise, is no more than a hypothetical ‘supposition’ or an ‘assumption’ that may prove to be false later on. There is no element of subjective belief in ‘assume’.
On the other hand, ‘presume’ refers to supposition with a hint of prior belief in it, even though there is no direct proof or clear-cut evidence to base this belief on. The belief stems probably from the knowledge that there is no evidence or proof to the contrary; or there may be some evidence pointing towards it that allows one to make an informed, reasonably intelligent guess.
When you ‘presume’ something to be true or otherwise, you believe in it until evidence to the contrary is presented. ‘Presume’ is associated with a higher degree of certainty and is thereby used in legal contexts. Thus, ‘presume’ is preferable to ‘assume’ if the supposition is supported by some amount of reasonable evidence, however small.
Sometimes the belief element in ‘presume’ may be reflected as overconfidence and hence may lend a connotation of arrogant or daring attitude to it. In this sense, ‘presume’ indicates ‘take liberties or be impudent enough’; that explains the origin of the adjective ‘presumptuous’. Another meaning of ‘presume’ when followed by ‘on’ or ‘upon’ – ‘presume on’ or ‘presume upon’ someone means to take undue advantage of someone’s good nature using unscrupulous means.
The word ‘assume’ can also have meanings other than ‘suppose’. ‘Assume’ can also mean ‘take upon oneself or put on oneself a role, attribute or attitude’, ‘to pretend or feign ignorance’, or ‘undertake the duties of an office’.
Here are some illustrative examples for ‘assume’ versus ‘presume’:
- Let us assume that the given mathematical statement is true for n = m.
- I assume that I have had my medication in the morning, though I do not remember whether I’ve had or not.
- I presume you to be the boss in this office, judging from other people’s attitude.
- Everyone presumed her to be innocent.
- He assumed the role of breadwinner of the family when his father expired.
- He presumed to invite himself to my party.
- The terrorists assumed control of the entire village.
- The problem of corruption has assumed great proportions.
These examples should suffice to illustrate the difference between ‘assume’ and ‘presume’.