These two words, often used interchangeably, are similar but the subtle differences are significant.
Both assume and presume mean “to take at face value” or “suppose,” but presume carries more weight based on past behavior or evidence. Assumption is to consider something valid without proof. Something you presume is more likely to be true than something you assume.
The website “The Grammerist” articulates the difference:
Both terms have a common root from Latin: Sūmere meaning “to take up.” The Latin assūmere means “to take to oneself; adopt.” Praesūmere, means “to take upon oneself beforehand; to anticipate.”
When I assume things are good in a relationship little space is left for growth. When I presume that my friend acts out of good intention, the door is wide open for encouragement. Assumptions tend to take the same old path, but presumption is like exploring new territory. The first often goes with out dialogue while the other opens the way for deeper understanding.
Call to en-Couragement: Invite a friend into conversation and share an assumption: “I have always assumed that because of your haircut you were in the military, is that so?” Once the response begins, invite them to go deeper by sharing several times the phrase “Tell me more.”