Deductive reasoning is useful both for rejecting and supporting hypotheses.

Deductive reasoning leads to conclusions based on premises that can be demonstrated to be true. Deductive reasoning is a central part of the "Hypothetico-Deductive" model for hypothesis testing and scientific discovery. However, deductive arguments must be valid and sound to lead to strong conclusions. 

How can we use deductive reasoning to test hypotheses? Deductive reasoning can be used to reject and to support hypotheses:

1) The logical syllogism modus tollens can reject hypotheses.

2) Strong inference using a tree structure can support hypotheses.