Journal Entry #9: Informal, Inductive and Deductive Reasoning

A syllogism is a logical appeal that is used in deductive reasoning. Deductive reasoning combines statements to determine facts, and consists of two premises and a conclusion. For example:

All cows eat grass.
Marley is a cow.
Therefore Marley eats grass.

What is interesting about deductive reasoning is that the conclusions that are derived may not necessarily be true in practice (because one or more of the clauses are untrue), however they may still be valid, and completely plausible when interpreted without any external knowledge. For example:

All pigs can fly.
I am a pig.
Therefore I can fly.

Whilst pigs cannot actually fly, the conclusion derived by deductive reasoning is valid because it logically follows the two premises that are stated. We use deductive reasoning in everyday life, however it is very easy for us to arrive at valid, yet untrue conclusions because some of the information we have used in our premises is incorrect.

Whilst deductive reasoning goes from the general to the specific, inductive reasoning goes from the specific to the general. Facts are determined from repeated observations. For example, you may notice that whenever you've dropped a pen, it's fallen towards the ground, which leads you to the conclusion that all pens fall downwards when released from a height above the ground. This form of reasoning is subject to human error and personal interpretation (as conclusions are derived from personal experiences). It can also be argued that due to uncertainties in our universe, we can not say that observations that have repeated themselves throughout our lives can be labelled as forgone conclusions. I will be talking about uncertainties in my next entry, which might help to expand on this idea.