word choice - Is there a difference between "continual" and "continuous"?

They are very close in meaning, I know, but I want to know if there are any subtle differences. Let me give you an example of a subtle difference in meaning between synonyms:

Deceitful vs. deceptive

At first glance, these seem to be perfect synonyms. However, in putting them into sentences, one finds a pattern - deceitful is almost always used of persons, and deceptive is always used of situations or things. So the "perfect" synonyms cannot always replace each other.

My question is: is there a similar subtle difference between continuous and continual?

Answer

Yes. Continuous means from some start to some end without break:

The water flowed continuously over the dam.

whereas continual means occurring repeatedly at intervals over a time span:

I continually lose at poker.

I should also mention that continual is often substituted for continuous, and would be correct in most contexts, however the converse is not generally true. That is to say,

The water flowed continually over the dam.

is okay, but you would (hopefully) not mean

I continuously lose at poker.

since that would imply that all you do all day long is play poker and lose.