The Difference Between Assume and Presume

Assume and presume both mean "to take something for granted" or "to take something as true," but the words differ in the degree of confidence the person assuming or presuming has. Presume is used when someone is making an informed guess based on reasonable evidence. Assume is used when the guess is based on little or no evidence.

Presume functions a little differently in the legal catchphrase "presumed innocent until proven guilty." That sense of presume is separately defined as "to suppose to be true without proof." It is based on the fact that legal systems grant a defendant the presumption of innocence, thereby placing the burden of proof on the prosecution.