Is "once you stop to think about it" ambiguous?

I tripped over a phrase in a book similar to "Once you stop to think about it, the existence of rainbows is pretty amazing."

Now, in context, it is pretty clear that I am supposed to stop my usual thoughtless existence to take some time thinking about rainbows, but literally, the phrase could mean that I should stop all this useless thinking to have time to appreciate rainbows more.

Is the phrase "stop to think about it" actually ambiguous or is it always used in the sense of thinking?

Solution 1:

No, it's not ambiguous. It's an idiom, and it has exactly the sense that you said was "pretty clear".

The thing is, stop only takes gerund complement clauses, and does not take infinitives.

• Stop hitting it!
• Have you stopped beating your dog?

When an infinitive clause occurs after stop -- in exactly the place it would if it were a complement (thank you very much, English syntax) -- it is not a complement (i.e, it's not what you're supposed to stop doing). Rather, it's a purpose infinitive (i.e, it's an adverbial clause explaining the purpose of your stopping).

You can tell the difference if you substitute an adverbial phrase for the infinitive.

• He stopped to hit the dog
  means
• He stopped ((doing something), in order) to hit the dog.

The idiom I mentioned in the first line is the once NP VP construction, as in

• I understood it once he showed me how it works.
• Once you eat durian, you'll see what all the fuss is about.

The VP has to be an event; pure stative predicates are interpreted as change-of-state events, which are called Inchoatives /ɪn'kowətɪvz/ in the trade; it's a great word to throw into a cocktail party conversation.

• Once she was tired, she took a rest.
• Once I own that house, I'll gut it.
• Once he's tall, he'll sink it every time he shoots.

... and, like all idioms, it sounds very weird after you repeat it a lot. Welcome to syntax.

Solution 2:

No, it’s not ambiguous. Anyone who wanted to express the thought I should stop all this useless thinking to have time to appreciate rainbows more would do so by beginning Once you stop thinking about it . . .

Solution 3:

Stop to think about it is used to describe pausing to further consider an issue, thing, etc. Example:

At first, Leonard's attitude seemed nice, but once I stopped to think about it, I realized he was actually being sarcastic.

Solution 4:

No, it's not ambiguous.

The phrase "I stop to think" means "I stop, in order to think", not "I stop thinking" (which is how you say the other meaning you were talking about).

But this isn't particular to the "once you stop to think about it" idiom, or indeed the verb "to think". In general, "stop to X" does not mean "stop doing X", it means "stop, in order to X". The action that is stopped is usually something defined earlier in the sentence (or by context); the X action is the reason you are stopping that other action.

Examples:

We were driving all day, except when we stopped to grab a bite to eat.

We don't stop grabbing (a bite), we stop driving in order to grab.

I exited the building, stopped to let a woman in a wheelchair pass, then crossed the street.

I don't stop letting (a woman in a wheelchair pass), I stop in order to let the woman pass.

Alice is eating a sandwich, but she stops to answer Bob's questions.

Alice doesn't stop answering (Bob's questions), she stops eating.