assume and presume....?

I assume you are asking me or I wouldn't presume to answer.

In many contexts when the meaning is 'to suppose', the two words are interchangeable: e.g. I assume/presume you are coming to the party. But, as the Pocket Fowler's Modern English Usage (Ed. Robert Allen. Oxford University Press, 1999) points out, '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.' The Oxford English Dictionary definitions are very similar. Assume is 'to take for granted as the basis of argument or action'; presume is 'to take for granted, to presuppose, to count upon'. There is a faint suggestion of presumptuousness about presume.

The New Oxford Dictionary of English which is based on recent usage evidence, provides these definitions:

assume suppose to be the case, without proof.

presume suppose that something is the case on the basis of probability; take for granted that something exists or is the case.