When to use an article before "reason"

Question

Please help me to understand when should I use an article before reason and when I should not use any article before reason.

Examples:

(A) I have reason to do this.

(B) I have a good reason to do this.

(C) I have a reason to do this.

(D) I have some reason to do this.

I meant to say all sentences in the same way, just want to confirm when should I use an article and when I should not. Please also check all sentences are correct or not.

Thanks in advance.

Answer 1

There are different uses of the noun "reason" here.

B,C,D) For these it is a countable noun.

I have reasons for doing this.

Note the use of the plural. This looks very similar to (A) but is using "reason" as a countable noun.

0) Another use of "reason" is an uncountable noun.

There is reason in madness.

A) Example (A) is a phrase "to have reason". Here "reason" means that what you do is reasonable, you could justify it. It is from the uncountable noun. So what you do can be justified.

I have reason to believe you.

I have good reason to do this.

Or you could justify the actions of someone else.

He has reason to do that.

Sometimes, you can justify your expectation of something even if it is not true or provably true,

He has reason to know.

Answer 2

This is interesting.

Grammatically, what is going on is that "reason" is being interpreted both as a "mass noun" (which never takes "a") in sentences (A) and (D) and as a "count noun" (which obligatorily takes "a") in sentences (B) and (C). "A reason" refers to one specific entity (I am doing this because it will cause me to earn 1000 dollars next year) whereas "reason" is more ambiguous, possibly refering to lots of "reasons" or to a reason that the speaker does not wish to specify.

Both (B) and (C) are fine and only differ by the word "good" which means something logical. To me (American) (A) sounds formal and (D) sounds wrong, or almost wrong, because we don't use the mass noun construction very often. In fact the only time I personally use it is in the specific phrase "I have reason to believe that [x]"

It would be interesting to hear from other speakers on this.