And faith is a deduction. A deduction is an inference in reverse.
I would think it more accurate to say that faith is an assumption. So, for example, the Christian Apologetics and Research Ministry offers:
Faith - Acceptance of ideals, beliefs, etc., which are not necessarily demonstrable through experimentation or reason. [
source]
Interestingly enough, they also suggest:
Deduction - A system of logic, inference and conclusion drawn from examination of facts. Conclusions drawn from the general down to the specific.
If one accepts these definitions as reasonable, then we see
'faith' defined as an acceptance of ideals, beliefs, etc., which are not necessarily deducible.
Of course one could, in the spirit of Humpty Dumpty, define
'faith' and
'deduction' in a way that supports one's presuppositions, but that's more comforting than constructive.