Yes, DIALECTIC is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, A 1, L 1, E 1, C 3, T 1, I 1, C 3.

Is it a valid word?

DIALECTIC is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any formal system of reasoning that arrives at the truth by the exchange of logical arguments
a contradiction of ideas that serves as the determining factor in their interaction