According to Bulgarian philosopher and literary theorist Tzvetan Todorov 1970 book The Fantastic: A Structural Approach to a Literary Genre (1970) the first question in genre theory is:

“Are we entitled to discuss a genre without having studied (or at least read) all the works wich constitute it [the corpus]?”

He answers the question with yes:

“Scientific method allows does not require us to observe every instance of a phenomenon in order to describe it; scientific method proceeds reather by deduction.”

But he also warns that:

“Whatever the number of phenomena (of literary works, in this case) studied, we are never justified in extrapolating universal laws from them.”

After which he goes on to quote Karl Popper and the famous black swan example of inductive vs deductive reasoning:

“no matter how many instances of white swans we have observed, this does not justify the conclusion that swans are white.”

See also: genre theory