Dave's ESL Cafe's Student Discussion Forums

[Koro]

I know an expression of gratitude: It's very kind of you ( to help me).

Grammatically, 'It' is a preparatory subject, which refers to to-infinitive. and 'of you' is the infinitive's own subject.
Then, with regard to the expression: That's very kind of you,
how should we explain this in terms of grammar? For example, if 'That' refers to some action of favor, I think it is impossible to consider 'of you' to be a subject of infinitive itself because we cannot put to-infinitive after the expression. I would really appreaciate it if you could teach me how we should grammatically explain this expression. Thanks in advance.
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Koro

[hitori2k6]

Koro,

When you're saying "that's very kind of you", the "that's" refers to
some action that both the speaker and listener are familiar with.

I gave my friend a ride to work and he said "That's very kind
of you" because both he and I are aware of the event.

Grammatically, I'm not sure how to explain why this is, but in
most cases if someone says "its very kind of you", they're more
likely referring to some event that is happening or will happen
in the future.
Whereas, "that's very kind of you" is more likely to be spoken
about some event that has already occured.

"its very kind of you to take me to the airport".

"That was very kind of you to invite me to dinner".

>>I hope this helps. I admit that it is very confusing
but its just the way English can be sometimes<<.