The Only Use

hypothesis
in
Flowers for Algernon -- Short Story
(Edited)

The hypothesis here proven may be described simply in the following terms: Artificially increased intelligence deteriorates at a rate of time directly proportional to the quantity of the increase.
p. 18.1

hypothesis = theory or belief (based upon limited evidence)

Definitions:

(1) (hypothesis as in: a study to test her hypothesis)
a seemingly reasonable, but unproven idea or explanation based upon known facts

In casual conversation, theory is a synonym for hypothesis, but a scientist would say that a hypothesis needs to pass rigorous tests before it could be accepted as a theory.
(2) (hypothesis as in: assume as a working hypothesis)
something that may or may not be true, but is temporarily treated as true to advance a discussion or to further investigation

This sense of hypothesis is typically seen in the form, hypothetical, or hypothetically.
(3) (meaning too rare to warrant focus)