When examining this apparent contradiction, one should consider the linguistic options in a Greek lexicon. The aorist infinitive dounai (of didomi) which the AV translates as 'to give' may also be rendered 'to grant'. See the BAGD lexicon entry for this fact. Thus, if the best rendering of dounai is in fact 'to grant' in the Matthean passage, then there is absolutely no argument for a contradiction here, for Jesus' words to the Sons of Thunder that 'to sit on my right and my left is not mine to grant' merely is a statement about the exercise of Jesus' authority in this particular matter, which does not at all contradict John 3:35. To pursue the argument further, one must somehow demonstrate that the ability to grant the seating at His right and left is a 'thing' in the same sense as John 3:35. Recalling that there is no direct word for 'things' (usually a neuter article or demonstrative is used in lieu of a Greek word for 'thing[s]'), it is unclear how this could be done.

If one instead favors the translation of dounai as 'to give' as the AV has it, the assertion rests on the mistaken premise that not being able to give something somehow necessitates that one does not have it in the first place. But this is in error. I have my life but I cannot give it to somebody... We see that there are situations (and it is not hard to think of them) where we have something but do not have the full freedom (for various possible reasons as in the examples) to give them. So, if Jesus states that the request is not his to grant, it does not at all follow that John 3:35 is contradicted.