It is often believed that valid/sound deductive arguments can provide certainty.  This is not quite true.  The conclusion of a valid/sound deductive argument is certain in the sense that it follows necessarily from the premises.  It does not mean, however, that the conclusion is certainly true.  Why?  The premises are usually contingent truths discovered inductively, and thus the veracity of the logically certain conclusion depends on the veracity of the probabilistic premises.  The more confidence we have in the truth of the premises, however, the more confidence we can have in the veracity of the conclusion.