incredulous

The third time I heard someone say, just in a matter of days, that such-and-such an event was incredulous (instead of incredible), I thought I should write about it.  There is no reason to confuse these two words.  It would be nice if we could keep them separate.

The starting point for both of them is the Latin credulus, an adjective formed from credo ‘I believe’ meaning ’believing too easily’, ‘trusting’.  Apparently Latin experienced its own switch in meaning to ‘worthy of belief’, ‘trusted’. Classical Latin maintained the first meaning but post-classical Latin allowed the second. Even in Latin meanings can be slippery.

In English we took the Latin credulus and added the English suffix -ous to it and kept the Latin meaning of ‘gullible’.  The other word, credible, was derived from Anglo-Norman credable and Middle  French credible with a nod to the original Latin credibilis meaning ‘able to be believed’. The familiar ending in -ible puts us on the right track.

Add the prefix in- in the sense of ‘not’ and you get incredulous ‘not believing easily’ and incredible ‘not able to be believed’.  Incredulous applies to a person who finds it difficult to believe something or to trust someone.  Things do not have the power to believe or trust.  On the other hand things can be incredible, scarcely able to be believed.

I hope this confusion is not too far gone for us to make a recovery.