Quick answer
Incredible describes the thing — hard to believe, or loosely, amazing. Incredulous describes the person — unwilling or unable to believe. A story is incredible; the listener is incredulous. Only people can be incredulous.
The core difference
The thing and the reaction to it.
- incredible — hard to believe: an incredible claim. Loosely: amazing.
- incredulous — disbelieving: an incredulous stare.
The pattern
This is the same shape as credible/credulous, which is worth learning alongside it. Something credible is believable; someone credulous believes too readily. So: -ible for the thing, -ulous for the person, in both pairs.
The weakened sense
Incredible has drifted to mean simply "excellent" — an incredible meal. That use is standard and unobjectionable, but it has eroded the literal sense, which is one reason writers reach for unbelievable when they mean it precisely.
Frequently asked questions
Can a thing be incredulous?
No. Only people can be incredulous. Things are incredible.
What is the difference between credible and credulous?
Credible means believable and describes a thing; credulous means too ready to believe and describes a person.
Is using incredible to mean "great" wrong?
No, that sense is standard — though it has weakened the literal meaning of hard-to-believe.
