Deductive reasoning is arriving at a specific statement by logical conclusions from a more general statement. If the logic is not fallacious the conclusion is necessarily always true.
The problem with deduction is that the general statement is not necessarily true. In fact there is no universal statement from which all our knowledge can be deduced. Usually we arrive at general statements by induction and use deduction further on. Some general statements are set by ideology without any empirical evidence, such as the existence of God. Unfortunately most scientists are unaware of the general statements that form the foundation of their reasoning. Those genral principles of science are called axiomas.
Fauceir Therory has developed its own axiomas. The induced general rules allow deductions which amazingly comply with reality.
