In deductive argument, the conclusion necessarily follows from the premises. The premises demonstrate the truth of the conclusion as they imply it.

On the other hand induction deals with those inferences which derive universal conclusions from instantial premises. Hence inductive arguments are not to be classified as valid or invalid which is a characteristic feature of deductive arguments.

But inductive arguments are characterized as probable, and there are degrees of probability. Again it should be noted that inductive logic does not formulate arguments, but studies the nature of inductive arguments with a view to laying bare the structure and procedure of generalizations.

Further it was noticed that the basis of primary induction is observation of particular instances. That is by observation or experiment of facts we are able to make inductive generalizations. Thus observation and experiment provide the material basis of induction.

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Again inductive leap is a very important feature of induction. Without inductive leap no inference can be characterized as truly inductive. Therefore having an inductive leap is considered as an essential feature of inductive generalization.

Further because of the leap involved in induction an inductive argument is considered probable. Since all inductions are about propositions relating to matters-of-fact such propositions lack analytical certainly.

Any such proposition is contingently true and its opposite is also a possibility. So probability is another important characteristic of an inductive generalization.

Thus having been based on observation of facts, having an inductive leap and having been about the world of facts and thereby being probable are the significant characteristics of induction proper.

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In absence of any of these characteristics no inference can be considered as induction proper. Hence any process of inference can be characterized as inductive if its conclusion is based on observation of instances, possesses an inductive leap, i.e. passes from some to all or observed to unobserved and is a real proposition which is only contingently true.

There are three such kinds of inference and they are scientific induction, unscientific induction analogy.

There are some simulating forms which give the appearance of being induction but are not inductions at all. Any inference that does not possess the essential features of induction is not an induction.

In some of the text books induction by complete enumeration, parity of reasoning and colligation of facts are named as induction-improperly-so-called. But since they are not to be classed as inductions calling them as induction is misleading. In induction by complete enumeration the conclusion does not possess any inductive leap for it is established after exhaustive enumeration.

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The conclusion here is a universal proposition based on observation of all facts connected with this induction. After individually verifying all the cases and subsuming them under one proposition a universal proposition is formed. So perfect induction by complete enumeration is more of a deductive argument than an inductive argument.

To make assertions like ‘every month of English calendar has less than thirty two days’, ‘every planet rotates round the sun’, ‘each student in a particular class knows English’ etc. are examples of this type of induction. Similarly in parity of reasoning the conclusion is a mathematical assertion deductively drawn from some theories or axiom.

Here it is taken that what-ever reasoning holds in a single case the same reasoning will apply in every other similar case. For example, after proving that the interior angles of a triangle are equal to two right tangles we generalize that the same reasoning will apply in case of every other triangle.

So there is a generalization that the interior angles of every triangle will make two right angles. But such an inference is not at all inductive for it is not based on any observation of facts. Since it is not based on any observation of facts, the conclusion reached here is not a real proposition.

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The conclusion is a mathematical proposition which is necessarily true. So most of the important characteristics of induction are lacking in induction by parity of reasoning. Similarly in colligation of facts a set of observed phenomena is brought under a notion or a class name. After going round a building one forms the idea that it is an educational institute.

In this form of reasoning new concepts are formed by binding together many observed facts. But no inductive leap is involved in this process of thinking.

Thus induction by complete enumeration, parity of reasoning and colligation of facts are not considered as induction and therefore are not discussed in this chapter which deals with induction as a form of inference.

Since they are only processes simulating inductions they will be dealt with a little elaboration in the chapter discussing Inductive Fallacies. Hence we shall discuss three basic forms of induction such as scientific induction, induction by simple enumeration or unscientific induction and analogy.