Fallacy means error in reasoning. Every inference involves some reasoning whether good or bad. Logic distinguishes good reasoning from bad reasoning. Logic also analyses the processes and principles governing all inferences. It lays bare the principles of valid inference.
Some logicians use the term fallacy in a wide sense to cover all errors that arise in logical discourses. Sometimes the term fallacy is used in a restricted sense to stand for erroneous inferences only.
It is not possible to classify and name all fallacies in an exhaustive way. Truth and validity may have their criteria but error and fallacy will have no limit. Fallacy has been discussed to guard against the logical errors either in inference or in other areas of logical discourse. Some fallacies are of very common occurrences and some are technical and fall under distinct types.
It has been customary to classify fallacies into two broad areas like deductive fallacy and inductive fallacy. Deductive fallacies are the logical errors, ambiguities or confusions which occur in respect of the subject matter of Deductive Logic about which we shall not be concerned here. But we shall discuss some important types of inductive fallacies that occur in respect of Inductive Logic. Further inductive fallacies, like the deductive ones, are classed as inferential, non-inferential and extra-logical.
The important types of non- inferential fallacies arise due to the violation of the rules or procedures connected with observation, hypothesis, explanation, classification etc. Such fallacies have been dealt with in their concerned sections and we shall not repeat them here.
Inferential fallacies arise when the rules of inductive inference are violated. They occur in the areas of causation, generalization and analogy. Extra-logical fallacies occur due to undue assumption of the premises, erroneous apprehension of the relation between the premises and conclusion etc. Petitio principii, ignoratio elenchi, fallacy of undue assumption is very common extra-logical fallacies. We shall discuss these fallacies and omit those which have already been discussed in different sections.