Sub-reason

noun
1.
a basis or cause, as for some belief, action, fact, event, etc.:
the reason for declaring war.
2.
a statement presented in justification or explanation of a belief or action:
I dare you to give me one good reason for quitting school!
3.
the mental powers concerned with forming conclusions, judgments, or inferences:
Effective leadership requires a person of reason.
4.
sound judgment; good sense.
5.
normal or sound powers of mind; sanity.
6.
Logic. a premise of an argument.
7.
Philosophy.

the faculty or power of acquiring intellectual knowledge, either by direct understanding of first principles or by argument.
the power of intelligent and dispassionate thought, or of conduct influenced by such thought.
Kantianism. the faculty by which the ideas of pure reason are created.

verb (used without object)
8.
to think or argue in a logical manner.
9.
to form conclusions, judgments, or inferences from facts or premises.
10.
to urge reasons which should determine belief or action.
verb (used with object)
11.
to think through logically, as a problem (often followed by out).
12.
to conclude or infer.
13.
to convince, persuade, etc., by reasoning.
14.
to support with reasons.
Idioms
15.
bring (someone) to reason, to induce a change of opinion in (someone) through presentation of arguments; convince:
The mother tried to bring her rebellious daughter to reason.
16.
by reason of, on account of; because of:
He was consulted about the problem by reason of his long experience.
17.
in / within reason, in accord with reason; justifiable; proper:
She tried to keep her demands in reason.
18.
stand to reason, to be clear, obvious, or logical:
With such an upbringing it stands to reason that the child will be spoiled.
19.
with reason, with justification; properly:
The government is concerned about the latest crisis, and with reason.
noun
1.
the faculty of rational argument, deduction, judgment, etc
2.
sound mind; sanity
3.
a cause or motive, as for a belief, action, etc
4.
an argument in favour of or a justification for something
5.
(philosophy) the intellect regarded as a source of knowledge, as contrasted with experience
6.
(logic) grounds for a belief; a premise of an argument supporting that belief
7.
by reason of, because of
8.
in reason, within reason, within moderate or justifiable bounds
9.
it stands to reason, it is logical or obvious: it stands to reason that he will lose
10.
listen to reason, to be persuaded peaceably
11.
reasons of State, political justifications for an immoral act
verb
12.
(when transitive, takes a clause as object) to think logically or draw (logical conclusions) from facts or premises
13.
(intransitive) usually foll by with. to urge or seek to persuade by reasoning
14.
(transitive) often foll by out. to work out or resolve (a problem) by reasoning