1. I saw John running to the classroom.
2. I saw John run to the classroom.
Which one is correct?
in formal written english, sentences like #1 are actually incorrect, for at least one (and possibly both) of the following 2 reasons:
(a) ambiguity
this is the problem with this particular sentence #1: it could mean what you want it to mean, but it could also mean that you saw john while you were running to the classroom. this will happen with most situations involving verbs of perception (such as "saw" here). （我认为这里就算ambiguous也是因为running作修饰语修饰john，为毛是我跑撒~~~~）
(b) incorrect reference because you need a possessive
for instance, you can't write "everyone laughed at me going into the girls' bathroom by mistake". weirdly enough, the correct form here is possessive: "everyone laughed at my going into the girls' bathroom by mistake". the former version would actually mean, unambiguously, that everyone laughed at me while they went into the girls' bathroom by mistake. （这里的错误点难道不是错误的表达为everyone 笑的不是这件事而是我么~毕竟going没有逗号修饰的是me 撒~~~，怎么会变成they going ????)
#2 is better because it's unambiguous, and because it actually communicates your intended meaning.
