What is the difference between such and such as?
The use of such as is relatively simple. It is used with a noun to introduce examples:
He likes playing sports such as tennis, football and swimming.
At such times as Christmas and Easter, many people take holidays.
The use of such is more complicated. In Practical English Usage (Michael Swan, Oxford University Press), the following principle uses of such are described:
1) In the formal style, such + noun can be used to mean ‘like this / that’ or ‘of the kind that has just been mentioned’. Such comes before a / an.
The committee is thinking of raising the subscription. I would oppose such a decision.
There are various ways of composing secret messages. Such systems are called ‘codes’ or ‘ciphers’.
2) Such is often used when we are talking about a high degree of some quality – in situations where very is also a suitable word. In this sense, such is common before adjective + noun.
I’m sorry you had such a bad journey. (= You had a very bad journey, and I’m sorry).
It was a pleasure to meet such interesting people.
3) In an informal style, such can also be used to give new information, when the speaker wishes to emphasise what is said.
He’s such an idiot!
She has such a marvellous voice!
Note also the difference between such and so. We use such before a noun (with or without an adjective).
It’s such good weather at the moment
They are such clowns!
We use so before an adjective on its own (without a noun) or an adverb.
The weather is so good at the moment.
Please don’t speak so quickly.