When do you presume, and when do you assume? These two words are often used interchangeably, likely because they come from the same Latin root and are used in similar contexts. However, there are subtle differences in meaning between the two. Today we put all assumptions aside, and get to the bottom presume and assume.
Both of these terms mean “to take for granted” or “suppose,” but presume conveys a little more confidence based on probability, reasonable grounds, or evidence. Assume is to take for granted without proof. In other words, something you presume is more likely to be true than something you assume.
Both terms derive from the Latin sūmere meaning “to take up.” The Latin assūmere means “to take to oneself; adopt.” Praesūmere, incorporating the prefix prae- meaning “before,” means “to take upon oneself beforehand; to anticipate.”
The famous expression “Dr. Livingston, I presume” sheds further light on the difference between these terms. This line was delivered by British American journalist and explorer Sir Henry Morton Stanley in 1871 when he arrived in Tanzania and located David Livingstone, a Scottish missionary and explorer whom several search parties had been sent to find as he had not been heard from for several years. Upon meeting Livingstone, Stanley remarked, “Dr. Livingstone, I presume.” Stanley’s use of presume is appropriate because Livingstone was, at the time, the only white European in the area, giving Stanley reasonable grounds on which to make such a presumption.
If you still aren’t sure how presume and assume are really any different, you aren’t alone. The key to deciphering between assume and presume is to understand that these two terms convey different degrees of certainty. However, in modern English, presume and assume are considered close enough in meaning to stand as substitutes for one another when you want to say “to take something as true,” so rest assured that your audience will still understand the intention of your sentence if you accidentally confuse the two.
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