assume, presume
1. Both words can mean ‘suppose’ and are often interchangeable in this meaning. Fowler (1926) maintained that there is a stronger element of postulation or hypothesis in assume and of a belief held on the basis of external evidence in presume, but in practice the uses are not always that distinct. Both words can be followed by a that-clause (or one with that omitted), by an object followed by a to-infinitive, or by a simple object: (assume)

• Throughout the book…the authors assume the validity of neo-classical economics as taught in the United States —Times Literary Supplement, 1974

• When you're young you assume everybody old knows what they're doing —Martin Amis, 1987

• This is assumed to refer to some sort of demonstration similar to April's Peking riot —Daily Telegraph, 1976

• (presume) I often hear the ungrammatical term ‘one pence’. I presume this is because the occurrence of a single penny is becoming a thing of the past —Daily Telegraph, 1974

• The Able Criminal…may be presumed…to be emotionally stable and ‘well-adjusted’ —Eric Ambler, 1977.

2. Assume and presume also coincide in a range of meaning that may be summarized as ‘to take on oneself’, although you generally assume roles and identities but presume attitudes and bearings. The intransitive use with a to infinitive is available only with presume. Examples:

• He was writing ‘Gerontion’, a dramatic monologue in which he assumes the persona of the ‘little old man’ —Peter Ackroyd, 1984

• He looked surprised —almost annoyed —as if a servant had presumed too great a familiarity —P. P. Read, 1981

• It is a reckless ambassador who would presume to preempt his chiefs —Henry Kissinger, 1979.

Modern English usage. 2014.