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According to Merriam-Webster, presume means

  1. to expect or assume especially with confidence
  2. to suppose to be true without proof

while assume means

  1. to pretend to have or be
  2. to take as granted or true

Does it mean they are somewhat synonymous and can be used in a sentence interchangeably? For example,

Students, tomorrow we will have a school activity, therefore we will have no Science class. However, there will be checking of attendance at 8:00 in the morning. I'll assume/presume that you are absent the whole day if your names are not on the list.

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    Yes, they are "somewhat synonymous". But idiomatically native speakers would almost always say I will assume [default assumption] if [a certain condition arises]. I think this may be something to do with the fact that the hypothetical condition and reaction are in a possible future, since I presume you were absent yesterday, since your name isn't on the list is far more acceptable to me (but still probably less common than the assume version). But there's probably more to it than that. – FumbleFingers Jul 2 '15 at 16:24
  • To presume involves presumption and is therefore presumptuous there is no corresponding assumptuous – Jim Jul 2 '15 at 22:13
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The words can often be used interchangeably. They have subtly different meanings that you should keep in mind when using them -- but don't assume a speaker or writer who is using them understands the difference!

"Assume" implies a bit more finality than "presume." It is more appropriate when a decision has been made, or is about to be made, with incomplete information.

"We didn't know how many people would be at the event, so we assumed that 100 chairs would be enough. (the decision was made)
"Since you didn't reply to my earlier email, I assume that you will not be joining us at the meeting." (implies that the speaker is ready to act without additional feedback from the recipient)

"Presume" gives a bit more room for the listener to correct the speaker. Using "presume" instead of "assume" adds an implied "but correct me if I am wrong" to the end of a statement.

"I presume you want chicken for dinner[, but correct me if I am wrong]."

In the past tense, "presumed" carries a bit of humility (if referring to oneself) or judgment (if referring to someone else), and it may imply that the presumption was incorrect in hindsight.

"I presumed that she would not object[, but she did object]."
"They presumed to know my intentions[, but they did not]."

"Assumed" is more neutral, and does not imply anything about the outcome of the assumption. If you want to communicate that the assumption was correct or incorrect, that fact will need to be made explicit.

"I assumed that the dog would not bite. I was wrong."
"She assumed that there would be enough cookies, and she was right."

The following examples contrast the two words and explain their implications:

Present tense:
"You have not told me what kind of ice cream you want. I assume vanilla will be fine."
(Even if the listener says nothing, the speaker will give them vanilla ice cream)

"You have not told me what kind of ice cream you want. I presume vanilla will be fine."
(The speaker would like the listener to confirm or reject the presumption. They will probably wait for an answer before giving the listener any ice cream)

Past tense:
"Alice assumed I would like chocolate cake for my birthday."
(The speaker may or may not have liked chocolate cake. It would be risky to guess without more information)

"Alice presumed I would like chocolate cake for my birthday."
(This is a subtly judgmental statement. Alice probably got it wrong.)

Final Disclaimer:
All of this is based upon present day, American usage. The words could carry different connotations in other countries or in older usage.

  • In fact I think slightly the opposite, Presumption involves taking liberties that might not really be one’s to take and so rather than humility it might be considered slightly rude. presume is often collocated with how dare you: ‘How dare you presume to know what I might like or dislike!” – Jim Jul 3 '15 at 1:54
  • @Jim, I think we are actually in agreement. Presume in the present tense is slightly rude, while presume in the past tense is more an of an admission of past rudeness -- hence the humility. – Jesse Jul 3 '15 at 22:23
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I would say both Latin verbs are synonymous with assume being more common. So we can express the same idea with to suppose/assume/presume (arranged in order of frequency).

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