May 24, 1997 Deduction and Induction
In Logic we are studying the ways of distinguishing correct from incorrect reasoning. We will be examining and focusing upon whether or not the premises justify the attempted conclusion of an argument. There are two basic kinds of argument: deductive and inductive.
Deductive argument asserts that the conclusion follows necessarily from the truth of the premises. For example:
All men are mortal. Joe is a man. Therefore Joe is mortal. If the first two statements are true, then the conclusion must be true.
Inductive argument asserts that the conclusion follows, not necessarily, but only probably from the truth of the premises. For example:
This cat is black. That cat is black A third cat is black. Therefore all cats are are black.
This marble from the bag is black. . That marble from the bag is black. A third marble from the bag is black. Therefore all the marbles in the bag black. .
Neither of the above examples has a conclusion that follows with necessity from the truth of the premisses. The conclusion can be false in each case, and the premises will still remain true. All we need is one exception to the general statement "All cats are black", all we need is one white cat, to show that the conclusion does not follow with necessity from the premises. However, inductive arguments are different than deductive arguments. Deductive arguments attempt to conclude with necessity, but inductive arguments do not attempt to do so. Inductive argument arguments only attempt to conclude with probability.
from: http://falcon.jmu.edu/~omearawm/deduction.html