watch?v=oBnKgxcdSyM 
[00:00:05.17] PROFESSOR: Deductive reasoning is reasoning that starts with a given set of premises and draws a conclusion. Deductive reasoning basically goes from general to specific. It starts with a given set of premises and draws conclusions from them. 
[00:00:19.76] The conclusions are only as valid as the set of premises that are used. And it only takes one false premise to produce a false conclusion. In a valid deductive argument, its truth necessarily follows from the starting premises. It is considered sound if it is valid and if all of its premises are true. Otherwise, it is considered unsound. 
[00:00:41.88] A common form of deductive reasoning is called a syllogism. It has three parts. A general characteristic of a category of objects, all x has y. The object under discussion belongs to the category, a is x. And concludes that the object under discussion has that general characteristic, a has y. 
[00:01:00.43] A critical point about deductive reasoning is that it is heavily dependent on the validity of the premises that are used. Premises may be a fact derived from observation or a totally philosophical assumption. 
[00:01:13.55] An example of this problem comes from proponents of the Big Bang cosmology. All observations of the universe are consistent with the Earth being near the center. Starting with the purely philosophical assumption that we are totally the result of natural processes as opposed to being created by God, they then make the logically valid conclusion that we cannot be in a special place in the universe such as the center. So they invented an explanation for the evidence that eliminates the center by making all locations in the universe seem to be at the center. If, on the other hand, we were created by God, then we could easily be near the center of the universe. This shows why creationists and evolutionists can look at the same evidence and draw totally different conclusions. 
[00:01:57.86] In conclusion, deductive reasoning is a useful tool of reasoning. It does, however, have its difficulties. It depends heavily on the accuracy of the starting premises, and flawed premises result in flawed conclusions. These difficulties need to be properly understood to properly understand scientific statements. This includes those of both creationists and evolutionist.