Accent and dialect are the subject in dialectology, sociolinguistics, linguistic geography and historical linguistics to which phonetics makes a contribution^ but which in themselves are not traditionally central to phonetics as such.
An important initial distinction needs to be introduced between 'accent' ^ and 'dialect'.
English is a language which has its own literature, its own grammar and its own dictionaries. It is also a language which is quite clearly not French, not German, not Chinese - or any other language. But to talk about the English language does actually mean something.
The point is that English -like all other languages - comes in many different forms, particularly when we think of the spoken language. Anyone can tell that the English of the British Isles is different from the English of the United States or Australia. The English of England is clearly different from the English of Scotland or Wales. The English of Lancashire is noticeably different from the English of Northumberland or Kent. And the English of Liverpool is not the same as the English of Manchester. There is very considerable regional variation within the English language as it is spoken in different parts of the British Isles and different parts of the world. The fact is that the way you speak English has a lot to do with where you are from - where you grew up and first learnt your language. If you grew up in Liverpool, your English will be different from the English of Manchester, which will in turn be different from the English of London, and so on.
People speak different kinds of English depending on what kind of social background they come from, so that some Liverpool speakers may be 'more Liverpudlian' than others. Some speakers may even be so 'posh' that it is not possible to tell where they come from at all.
These social and geographical kinds of language are known as dialects. Dialects, then, have to do with a speaker's social and geographical origins. It is important to emphasise that everybody speaks a dialect. Dialects are not peculiar or old-fashioned ways of speaking. They are not something which only other people have. Just as everybody comes from somewhere and has a particular kind of social background, so everybody - speaks a dialect. А dialect is the particular combination of words, pronunciations and grammatical forms that you share with other people from your area and your social background, and that differs in certain ways from the combination used by people from other areas and backgrounds.
It is also important to point out that none of these combinations -none of these dialects - is linguistically superior in any way to any other. We may as individuals be rather fond of our own dialect. Dialects are not good or bad, nice or nasty, right or wrong - they are just different from one another, and it is the mark of a civilised society that it tolerates different dialects just as it tolerates different races, religions and sexes. American English is not better - or worse - than British English. The dialect of ВВС newsreaders is not linguistically superior to the dialect of Bristol dockers or Suffolk farmworkers. There is nothing you can do or say in one dialect that you cannot do or say in another dialect.
Scientists who study dialects - dialectologists - start from the assumption that all dialects are linguistically equal. What dialectologists are interested in are differences between dialects.