  We can trace the fundamental source of Russell's restrictivism about acquaintance to the claim that one is acquainted only with that for which misidentification is rationally impossible. If it is possible for one to be presented with o twice over and rationally not realize it as the same object, then one is not acquainted with o; one's thoughts about o are, in that case, indirect. This line of reasoning relies on the Fregean claim that identity confusions are to be explained in terms of differences in thought constituents. Our English student's confusion regarding Mark Twain is thus to be explained in terms of different thoughts and hence different thought constituents corresponding to the different ways of thinking about the man Mark Twain associated with the expressions ‘Mark Twain’ and ‘Samuel Clemens’. This — that cases of misidentification always involve differences in thought contents — marks an important point of agreement between Frege and Russell.