Assume and presume are commonly used to mean the same thing – to suppose. However, the subtle difference lies in the level of certainty.
Assume implies less certainty; a supposition without proof or evidence.
- I just assumed more people would come.
Presume implies more certainty; a supposition after weighing probabilities.
- I presumed more people would come after I specifically invited them.
Assume and presume also share another meaning; to adopt a position or to take on oneself.
- She assumed the role of leader.
- She presumed too little dissatisfaction within her team.