cogent, good, sound, strong
compelling, convincing
plausible
adequate, sufficient
bona fide, legitimate, valid
wrong
He married her for all the wrong reasons.

opposite
Tom's problem was that he lacked confidence; Ed failed for precisely the opposite reason.

important
special
big, chief, key, main, major, primary, principal
There's one big reason why this won't work: cost.

only, simple, sole
The only reason I didn't become a professional golfer was because of my family commitments.
I was never good at school for the simple reason that I never studied.

several, various
I can think of several reasons why this might happen.

common
Isolation and loneliness are common reasons for depression.

real, underlying
She did not tell him the real reason for her change of heart.
The underlying reasons for these differences will be explored in depth in the next chapter.

possible
cited, ostensible, stated
The company's stated reason for firing him was misconduct.

exact, very
You're asking me to help, and that's the exact reason I came.

apparent, particular
He was attacked for no apparent reason.

no earthly, no possible
Surely there is no earthly reason why you wouldn't want to come with us?

clear, obvious
The reasons for her decision soon became clear.

unclear
logical, rational
understandable
justifiable
unspecified
unconnected
dismissal for reasons unconnected with misconduct

personal
sentimental
selfish
professional
commercial, economic, financial, legal, political, social, technical
practical, pragmatic
security
health
altruistic, humanitarian

be aware of, see
He saw many reasons to be hopeful.

have
I don't know why he did that, but I'm sure he had his reasons.
I have no reason to believe that she was lying to me.

cite, give (sb/sth), outline, provide, set out, state
Give me one good reason why I should help you.
In the letter she carefully set out her reasons for leaving.

list
This article lists the most common reasons why people pay too much tax.

offer, suggest
articulate, explain
cite sth as, give sth as, offer sth as
discuss, explore
understand
guess
discover, find, find out, uncover
pinpoint
It's difficult to pinpoint the reasons for her success.

by reason of (formal)
persons in need of care by reason of (= because of) old age
He was found not guilty by reason of insanity. (law)

for a/the reason
procedures carried out for reasons of national security

for reason of (formal)
For reasons of security, you are requested to keep your baggage with you at all times.

with reason, without reason
They complained about the food, and with good reason (= rightly).

reason against
There are obvious reasons against such a move.

reason behind
We are trying to uncover the reasons behind her decision.

reason for
They didn't give any reason for the delay.

all the more reason
If he's unwell, that's all the more reason to go and see him.

all sorts of reasons
People buy things for all sorts of reasons.

every reason, little reason, some reason
I know you're angry with me, and you have every reason (= very good reasons) to be.
You have little reason to be pleased with yourself.

no reason, not any reason
He got angry for no reason.
You don't have any reason to complain.

for reasons best known to yourself
For reasons best known to herself she has turned down the offer.

for some inexplicable reason, for some odd reason, for some strange reason, for some unfathomable reason
For some odd reason, he found it really funny.

for unexplained reasons, for unknown reasons
For unknown reasons, the ship sank in the middle of the ocean.

for whatever reason
people who, for whatever reason, are unable to support themselves

a number of reasons, a variety of reasons
rhyme or reason
There's no rhyme or reason (= logic) to the new opening hours.

not see any reason, see no reason
We see no reason why this band shouldn't be a huge success.
I don't see any reason why you can't come with us.

there is ample reason, there are ample reasons
There is ample reason to be optimistic about the economy.

human

lose
He seems to have lost all sense and reason.

be open to, listen to, see
I tried to persuade her, but she just wouldn't listen to reason.

defy
Sometimes he does things that defy reason.

beyond reason
He was beyond all reason.

within reason
I'll lend you the money you need—within reason, of course!

an appeal to reason
The residents hope that an appeal to reason (= asking the rioters to be reasonable) will end the rioting.

faculty of reason, sense of reason
We possess the human faculty of reason.

it stands to reason
It stands to reason (= it is logical) that she wouldn't want them to find out about her personal problems.

the voice of reason
She was always the voice of reason, persuading him not to buy things they couldn't afford.