Deductive reasoning involves deriving specific predictions from general principles, following a top-down approach which leads to testable hypotheses, while inductive reasoning formulates general theories from specific observations using a bottom-up approach. Both methods are essential in the scientific process, with deductive reasoning providing logical certainty if premises are accurate, and inductive reasoning being valuable for exploring new phenomena despite its probabilistic nature. Ultimately, effective scientific inquiry often incorporates both reasoning styles to develop and refine theories.