Assume or Presume

What's the difference?



1/23/20242 min read

In the last post, I joked that I never assume and only presume. Why? Because it makes no sense to say “when you presume, you make a ‘pres’ out of ‘u’ and ‘me’”. So that got me to thinking about what is the actual difference between “assume” and “presume”? According to, here is the difference between the two:

Assume – to suppose without reason or evidence.

Presume – to suppose something with some probability or evidence.

Given that distinction, my smart aleck comment to never assume and only presume could be considered good advice. We have to make determinations about things without complete knowledge very often, so try to make decisions when you have good reasons to do so. Also, I am going to presume that people often say assume when they more properly should say presume. In my experience people usually have some merit for their suppositions.

In light of those differences, it is interesting that being “presumptuous” is usually considered negative, even though when you presume, you have good reason for it. In fact, it is when someone assumes too much that they are described as presumptuous. Go figure. To clean up our language usage, I was going to propose a new word, “assumptuous”, to use instead. Then I discovered “assumptious” already existed. I have never heard of it, and it means – you guessed it – presumptuous. Isn’t that a rather circular definition? And why the different spelling? I have no idea and will let someone else take that on as a question to answer.

Worth noting, there are other definitions of the two words that have clearer use cases. If my boss was on vacation, I might assume, or take on, his responsibilities while gone. When used in a legal sense, presume means accepting that something is true when there is no proof that it is false. The most common used is that the accused are presumed innocent until proven guilty. Interestingly, in the non-legal sense, it may be proper to presume someone is guilty because there is good reason to do so. They wouldn’t be on trial if there was no evidence.