What word or phrase describes the quality of an assertion to be inbetween a fact and an opinion?

Solution 1:

A hypothesis is a guess, based on data or logic of some kind.

So, if your hypothesis is: It is pointless to brush your teeth in the morning because no food has been eaten, not eating serves as the logic that bolsters your guess.

For a hypothesis to be viable, it needs be testable.

Solution 2:

Theory comes to mind

An assumption based on limited information or knowledge; a conjecture.

Synonyms: hypothesis, thesis, conjecture, supposition, speculation, postulation, postulate, proposition, premise, surmise, assumption, presupposition;