1- I saw him to climb up the tree.
2- I saw him climbing up the tree.
Please, explain the difference in the meaning of the two sentences.
I imagine the mistaken 'to' was due to a misinterpreted rule (assuming 'infinitve' meant 'to-infinitive' and not 'bare infinitive'.)
Incidentally, the word is 'participle'. The OP's probably confusing it with 'principle' (which does have a '-pal' variant [but with an only distantly related meaning]).