Is there a difference between these sentences?

[theincrediblealfonso]

It was a sunny day, for which I was grateful.

It was a sunny day and I was grateful for it.

My niece has homework asking her correct the sentence "It was a sunny day that I was grateful for." and it has flummoxed everyone in our house!

Reading my first sentence again, does it even need the comma? My own sentence structure is guesswork so I'm clueless!

It was a sunny day, which I was grateful for.

...For which I was grateful

I was grateful that it was a sunny day.

I think they both look ok

Agree with taking chances - you shouldn't end a sentence with a preposition. 'For' is a preposition.

... For which I was grateful.

Sentences in English aren't meant to end on a preposition, though this is a bit of a nonsensical rule (I think it's a Latin rule applied to a English by over-zealous 19th century grammarians).

I was grateful for the sunny day.

It was a sunny day, which I was grateful for.

use the word which, not that.

Either of your answers would be correct, I think, as long as the sentence doesn't end in 'for'. It's pedantic, but this is Pedants Corner!

It's the "that" in the homework sentence which is wrong, because it's in a non-defining relative clause which only uses "which"

The two sentences in the OP are both perfectly correct, although the first one is more "formally" correct.

This is so confusing

The which/that thing is not too confusing once you've grasped it.

Compare these two:

This is the house, which Jack built.
This is the house that Jack built.

In the former, the main clause is "This is the house", and ", which Jack built" is a subclause and of lesser importance. The fact that Jack built it is slightly by the way.

In the latter, the fact that Jack built the house is the important thing: THIS is the house that Jack built. As opposed to another house.

I don't know how good a job I've done there. Hope it helps, but I may have confused you further.

Oh, and the two sentences you've put in your OP are fine, though I prefer the former - it's more elegant.

Ending a sentence in a preposition is, as people say, more likely to be wrong than right. You can do it, but you need a good ear to hear whether it's OK or not. "A sunny day that I was grateful for" isn't really OK because it's easily and elegantly avoidable.

It does clear thing up a bit Mrs Steptoe, thanks.

Asking this has made me realise how woeful my knowledge of grammar is!

Can anyone explain when you should use 'that' and when you should use 'which'? Is there straightforward rule?

Have a go at Grammar Girl's Quick and Dirty Tips. She's got quite a good way of explaining things.

www.quickanddirtytips.com/education/grammar/which-versus-that-0

Try not to be derailed by the use of technical grammatical terms but look at the examples and see if it gradually starts to make sense. If you google "that versus which" and look at several sites, the different explanations may sort of start to fuse into something that makes sense as well - sometimes if you read the same thing described by different people a few times, a light bulb goes off.

*Or does it go on? On, I think

Alfonso, that and which are interchangeable, but only in defining relative clauses.

The house which I told you about is green
The house that I told you about is green

In both of these sentences we can presume there is more than one house around, but one of them, the one that/which I told you about, is the green one. I am defining which house is being talked about

The house, which stood on the hill, was green

Here, you cannot use "that" because "which" introduces a non-defining relative clause. There is only one house, the green one, the fact that is on the hill is "extra information" which is why it is enclosed in commas. I could remove "which stood on the hill" and it wouldn't substantially alter the sentence.

It is easy enough in simple sentences to spot defining/non defining relative clauses, as long as the commas are used!

My sister, who is a nurse, lives in London
My sister who is a nurse lives in London

I give those 2 sentences to my students and ask them to tell me how many sisters I have.

In the first, I only have 1, in the second we don't know exactly, but more than 1, because in the first sentence, the fact that she is a nurse is an "extra information" clause whereas in the second it defines which sister is being talked about.

(nothing to do with which/that, but explains relative clauses a bit better)

Thanks for the link Mrs Steptoe

OMG, DrankSangria, the sister/ nurse sentences make things so much clearer. I get bogged down by the labels (didn't know what a relative clause was) because I don't know a lot so the examples really made it understandable.

I was googling this kind of stuff and now I'm looking up how to use semi-colons. Somehow I've got this far in my life without using one

We need to get over our fear of ending sentences with prepositions.

blog.oxforddictionaries.com/2011/11/grammar-myths-prepositions/

Ending sentences with prepositions is a grammatical error up with which we must not put.

The first sentence in the OP is better, according to strict pedantic grammar rules. You can debate the sense of enforcing these rules as clearly they are less and less relevant to the English language as it is currently actually spoken, but if your niece is going to be marked on the basis of how well she can remember and apply these rules then that is a debate to leave for now. Perhaps you can raise the debatability of these rules after the point on her school career when her overall academic achievement levels are going to be affected by this.

First rule: Do not use semicolons [...] All they do is show you've been to college. - Vonnegut

I agree with 2048. I would use the most excruciatingly correct option for school.