It is sometimes argued that the fact that possession of perfect knowledge about the future is impossible, means that it is impossible for decisions to be rational. This reasoning is fallacious. If rationality is given a new interpretation, then decisions can be considered rational. A theory of decision that has as its basis Peirce’s theory of abduction can provide a new way of understanding decisions as rational processes. The Peircean theory of decision (i) considers decisions as part of a complete strategy, and (ii) shows that decision making is governed by the same rules as scientific abduction. These rules are neither permissive rules like rules of deductive inference nor predictive like laws of nature, but rather genuine laws of conduct that determine what step should be made, if a given end is to be reached.