subject verb agreement

[morishimarisu]

"It is always sad to see someone you love die."

In the above sentence, why is the final verb 'die' and not 'dies' when clearly the subject of 'die' is someone, and not you? How does one explain this simply and clearly to a second language learner?

Thank you.

[Marius Hancu]

Die is here (short/bare) infinitive, not indicative.

The infinitive is atemporal and impersonal, it does not flex for tense and person.

E.g. you're saying:

It was sad to see John die. [in the past
It is always sad to see someone you love die. [in the present
It'll always be sad to see someone you love die. [in the future

Dies is indicative mode, which traces the tense and the person, but isn't used here.

The verb see works this way:

see (direct object) (short infinitive, or ing-form, but we wouldn't discuss that here)

I saw John leave. [direct object: John, short infinitive: leave
I saw John leaving. [direct object: John, ing-form: leaving

[Marius Hancu]

Read this from the BBC about see, hear, etc:

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Both see and hear, and also notice and watch and other verbs of perception, can be followed by object + bare infinitive (i.e. without to) or by object + verb-ing.

http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv214.shtml
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Read the whole article, for you need it.

Also, buy Swan, Practical English Usage. It'll help you a lot.