Thursday, 17 April 2014

Critical Thinking 6: Deductive & Inductive Arguments

Higher Philosophy Podcast
Critical Thinking: Deductive & Inductive

This is available as an MP3 or to download as a podcast through iTunes
for Desktop and Apple devices, as well as PodcastHD for Android Devices.

As we now know a sound argument is the most reliable type of argument, being both valid and true. This type of argument is in fact a DEDUCTIVE argument. The goal of a deductive argument is an irrefutable conclusion. That being said, we must classify all types of arguments.

Consider the argument to the left. We can see that premise 1 leads you to premise 2, and in turn to the conclusion. It reads as valid. 

In algebraic form we have: If P→Q, P∴Q showing conclusively that it is indeed valid. As best as we can tell, not knowing who Fang really is, the premises are true which means it is also sound. This is a DEDUCTIVE argument.
Compare the above argument to the one on the right. There is no need to convert this to algebraic form as we can clearly see that the conclusion do not follow on from the premises. The argument is invalid. However, this is also an INDUCTIVE argument.

Notice the pattern that is present in both arguments. The DEDUCTIVE argument uses information about a whole category and applies it to a particular within that category. In the example the arguer is taking a fact about all dogs and applying it to one particular dog. We can visualise in our head why this would work.

In the INDUCTIVE example the argument takes information about a particular and tries to apply it to the whole category of what is being argued. In the example the arguer is taking a fact about one human and tries to apply it to all of humanity.

We sometimes frame inductive argument negatively. This misrepresents what they are actually trying to do. Deductive arguments may indeed be the gold standard as the conclusion is a guaranteed truth; however, reliability is a scale and we cannot dismiss information simply because it does not meet the shiny standard of deductivity.

Consider paracetamol. Every time you have had a headache and taken paracetamol it has worked. You could, then, claim that paracetamol stops headaches. This is clearly not deductive, as it is moving from a specific (your headache) to the general (all headaches). Widen the example, the drug would have been tested on animals, then a small cohort of humans before being declared safe for all to use. Using paracetamol may not be deductive but we cannot dismiss it simply based on this. We must find redeeming qualities in its use.

A deductive argument has a guaranteed conclusion an inductive argument has a PROBABLE conclusion.

Consider the adjacent argument. Granted the study is small, however, the argument can be convincing. Like validity, each premises naturally follows the last leading you to the expected conclusion. However, only deductive arguments can be valid. An inductive argument that is convincing, mainly due to its structure, is said to be STRONG.

A valid argument is good, but a sound argument is better. As with deductive arguments inductive arguments have an equivalent. If an indicative argument is strong and the premises are true then the argument is said to be COGENT.

It is easier here to draw a direct comparison between deductive and inductive arguments. As noted above deductive arguments take a proposition about a group and apply it to a specific part of the group, whereas inductive arguments apply a singular proposition to a larger group. This is how the argument is used. We can compare and contrast the difference between both types of argument from a Critical Thinking perspective.

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