# How to figure out whether Infinitive is being used to express cause or purpose

"He wept to see the desolation caused by the flood". Literally, this line seems making sense that he wept in order to see.

While it actually makes sense that he wept when he saw desolation.

How to decide when infinitive is expressing purpose(like,he came to see him) and when expressing cause(what above line actually means).

• No, it has nothing to do with purpose or time. The infinitival clause "to see the desolation caused by the flood" is a reason adjunct; it gives the reason that he wept. Dec 18, 2017 at 18:19
• Incidentally, there are two subtypes of adjunct of 'cause': purpose and reason. Your example belongs to the latter. Dec 18, 2017 at 19:57

A simpler (to my mind) substitution than the one proposed by Lambie is to expand purpose infinitives from "to" to "in order to".

I come in order to bury Caesar.

That makes sense right? That's a clue that it's an infinitive of purpose.

He wept in order to see the desolation caused by the flood.

Does that make any sense? Does crying help him see anything? That's a clue that the infinitive is not for purpose, but for cause.

• 'Purpose' adjuncts are a subtype of 'cause', the other being 'reason'. The latter type is used to express doing something / something happening as a consequence of an earlier event, which is the case with the OP's example. Dec 19, 2017 at 7:29

I laughed to see the kids playing in the snow.

Substitution: I laughed **when I saw the kids playing in the snow**. The substitution makes sense. Therefore, it is a cause.

You can decide which one it means through substitution:

"I come to bury Caesar." SUBSTITUTION: I come when I bury Caesar=does not make sense here.

• You'd think the phrasing "upon seeing" would be better but perhaps that's an antiquated style as the "upon" part is usually omitted. Dec 18, 2017 at 17:14
• I would not ask an ELL to use that. The point is to make it simpler, not harder. :) Dec 18, 2017 at 17:15
• Your version involves a shift in tense, which could be confusing too. Just presenting an alternative here. Dec 18, 2017 at 17:20
• No, I keep the tense used in the first verb. I laughed to see: I laughed when I saw. I wept to see=I wept when I saw. And with the Caesar quote, it clearly does not work. Dec 18, 2017 at 17:33
• For the first verb, yes, but "to see" vs. "I saw" was what I meant. Dec 18, 2017 at 17:38