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Types of argument: deductive and inductive

This article continues the discussion of the different types of argument that you may encounter, or wish to use, as part of your doctoral research and writing. As explained in previous articles, the point of an argument is to support a claim, giving the reader good reason to accept that the claim should be accepted. In this article, we will look specifically at the use of inductive and deductive arguments as ways of supporting a claim.

Deductive arguments are those arguments where the conclusion (claim) must be true provided its premises are true: the conclusion necessarily follows from the premises. Deductive arguments include the classic modus ponens and modus tollens forms. An example of modus ponens is:

If Policy A is unjust then it should not be implemented (If p (is true) then q (follows))

Policy A is unjust (p (is true)), therefore

Policy A should not be implemented (q (follows).

An example of a modus tollens argument is:

If Policy A is a bad policy, then it will have bad consequences (If p, then q).

Policy A did not have bad consequences (not q), therefore

Policy A is not a bad policy (not p).

While for deductive arguments, true premises guarantee a true conclusion, for inductive arguments, the premises provide no such guarantee. For an indicative argument, the intention is to provide strong premises that make it likely or probable that the conclusion is true. For an inductive argument, the conclusion does not necessarily follow from the premises. However, where an inductive argument is persuasive then the premises provide the reader with strong reasons to accept that the conclusion (claim) is likely to be true. An example is:

In a random sample of consumers, 75% preferred the taste of Brand A to four other leading brands. A second survey showed that taste was the most important indicator of choice when consumers buy a product. It is, therefore, very likely, that Brand A will be the preferred choice of consumers.

While deductive arguments provide the advantage of guaranteeing a true conclusion, in many cases inductive arguments may be necessary because the strength of the premises is insufficient to justify a certain conclusion. In such a situation, the important thing is to ensure that the premises are as robust as possible and that they support the claim being made. The PhD Consultancy has a wide range of experts who can help you to construct the arguments necessary to support your thesis.

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