LESSONS IN LOGIC: The Formal Meaning of ‘Necessary’

I have been trained in the formal use of logic.  Consequently, I have a tendency to use certain terms in the same way they are used in formal logic.  This post covers one of these terms that is important enough and which will occur often enough to warrant a specific post explaining how I am using a given term.

If and when you find one of my posts where I stress the term, ‘necessary,‘ I am using it in the strict logical sense.  In formal logic, ‘necessary‘ means:

Something is said to be necessary when a specific condition or conclusion must be present or follow.  Put another way, if someone says a condition or a conclusion is necessary, that means the condition must be present and/or the conclusion must be true.

For example:

If it is true that all males have XY chromosomes (which is true — by definition),

And Bill is a male,

It is ‘necessary‘ that Bill has XY chromosomes.

In this case, it is ‘necessary‘ for Bill to have XY chromosomes because having XY chromosomes is part of the definition of being ‘male.’

The take-away from this post is this: if I ever stress the necessity of something, I am saying it is absolutely necessary; that it must be true; there is no way around it; no exceptions — period!