Is there an accepted term for the idea that: "an idea's validity is increased by the number of proponents"

Question

Is there a field or term which can be used to describe conjecture on the notion that:

The validity of an idea is related to the number of proponents/opponents of the idea.

Such a field would concern (or, term would describe), the validity of statements such as:

I find it hard to agree with an idea which has so little support.

If it were false, then why do so many people believe it.

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I have also asked a related question:

Is there an accepted term for the idea that: “an idea's validity is increased with age”

Answer 1

This is known as the Argumentum Ad Populum.

Answer 2

The question is well asked, but if you're assuming that the quantity of followers is what validates a theory, you might as well live in the middle ages...

The branch of mathematics that study concepts like validity, satisfiability, tautologies, etc. is called "propositionnal logic". Propositions cannot determine the position of a single claim (statement), but it can decompose propositions in order to check the consistency of compound statements.

What this allows us to do is to build theories from theorems. For instance, you can claim that it's raining and propositionnal logic can't deny that. However, you can say something like "when it's raining, you get wet" and "it's raining". If you further say that "you are wet", it does not mean that it's raining, but if it rains, you get wet. Google "propositionnal logic" for more information.