6.Used before and after a non-defining relative clause, or a phrase in apposition, which gives more information about the noun itfollows:
The Pennine Hills, which have been a favourite with hikers for many years, are situated between Lancashire and Yorkshire.
Queen Elizabeth II, a very popular monarch, celebrated her Silver Jubilee in
1977.
(Note. No commas are used around a relative clause that defines the noun itfollows:
The hills thatseparate Lancashire from Yorkshire are called the Pennines.)
7. Sometimes used to separate main clauses linked by a conjunction (e.g. and, as. but, for, or), especially when the first clause is long:
We had been looking forward to meeting Sarah's husband, but discovered thathe was not as pleasant as we had hoped.
Also Conversation and Letters below.
:COLON
1. (Formal) Used after a main clause where the following statement illustrates or explains the content of that clause. It may be replaced by a semicolon or a full stop:
The garden had been neglected fora long time: it was overgrown and full of weeds.
2.Used before a long list, and often introduced by phrases such as: such as: forexample: for instance: in the following examples: as follows:
Your first aid kit should include the following items: cotton wool, lint, antiseptic lotion, sticking plaster, bandages and safetypins.
Also Letters and Quotations below.
;SEMICOLON
1.(Formal) Used to separate main clauses, not (usually) joined by a conjunction, which are considered so closely connected as to belong to one sentence:
The sun was setting now; the shadows were long.
He had neverbeen to Russia before; however, it had always been one ofhis life longambitions.
2.Used instead of a comma to separate from each other parts of a sentence that are already separated by commas:
There are two facts to consider: first, the weather; second, the expence.
-DASH
1.(Colloq.) Used instead of a colon or a semicolon to make the writing more vivid or dramatic:
Sirens blared, men shouted, andpeople crowded in to witness the scene - itwas chaos.
So you’ve been lying to me for years and years - how can I ever trust you again?
2.(Colloq.) Used singly or in pairs to separate extra information, an afterthought or a comment, in a vivid or dramatic way, from the rest of the sentence:
Schooldays are the happiest days of our lives - or so we are told.
Schooldays - or so we are told - are the happiest days of our lives.
(Note. In more formal usage, parentheses or commas replace dashes.)
Also Conversation below.