Here are some differences between American English (AmE) and British English (BrE) based on the book Practical English Usage, by Michael Swan.
One variety of English may have numerous forms acceptable to say something in particular whereas, in the “other” English, only one form is proper.
AmE: He just sang a song / He’s just sung a song
BrE: He’s just sung a song.
AmE: It looks like it is broken
BrE: It looks as if it is broken / It looks like it is broken
*Some irregular verbs do not have the same form in British and American English
Sometimes, a given word may have a different meaning depending on the variety of English that is used.
AmE: Mad is a synonym of crazy
BrE: Mad is a synonym of angry
And often, a different word is used in both Englishes to refer to the same idea.
The prepositions and participles may differ from a variety to another.
AmE: On a team
BrE: In a team
AmE: Tuesday through Sunday (to also possible)
BrE: Tuesday to Sunday
Some words are spelt in a different way in British English than in American English. Moreover, the suffixes are often subject to change between the two.
AmE: Analyze BrE: Analyse
AmE: Color BrE: Colour
AmE: Defense BrE: Defence
AmE: Program BrE: Programme
There are also differences in the speech between British and American English, mostly in pronunciation.
AmE: More nasal vowels than in BrE
BrE: The sound “o” is rounded short (dog)
AmE: Pronunciation of the sound made by a+consonant is pronounced /ae/
BrE: The pronunciation is different than in AmE for the sound of the vowel like in home, go, open.
AmE: “r” is pronounced no matter where it is positioned in the word.
BrE: “r” is pronounced only before a vowel sound.
AmE: The “t” and “d” are softer and lighter than in BrE.
BrE: The “u” sound (new, tune) is pronounced like /ju:/
BrE: The suffix –ile is pronounced with /aIl/
AmE: The suffix –ile is pronounced like /l/
AmE: Every syllable is pronounced in long words ending in –ary, -ery or –ory
AmE: The final vowel of a word borrowed to French is most of the time stressed
What is standard English?
The victory of King Alfred, in 878, brought the establishment of the government of Southern England in London. As time went by, the variety of English used by the King and its government became official and was used in law, business and literature which brought its “standard” level.
What is a dialect?
Dialects receive most of the time a negative thought from people because many of them think that it is an incorrect form of language. However a dialect refers to the forms of speech of actors of history (Germanic, Scandinavian). A dialect as a systematic grammar and it is called a dialect only because it has not been chosen to be official by authoritative people.
What are the characteristics of formal English as opposed to informal or spoken English?
Formal English is mostly used in situations where the speakers or writers are careful about the way they express themselves (business meetings, with strangers, conferences). On the other hand, informal English is most of the time used with siblings. On a general note, formal is mostly used in written English whereas informal is used in spoken situations. The choice between formal and informal is highly related to the situation and environment that surrounds the speaker or writer. Some words and expressions are neutral. In grammar, contractions in verbs and negatives are a sign of informality. Even the position of a preposition in a sentence can show the formal or informal usage (What class are you in?=informal). Leaving out words is another form of informal English (Seen Luke? Instead of saying Have you seen Luke?) Some words, verbs and expression are especially used depending in the level of language that is used (I beg your pardon? as opposed to What?).
Do languages change over time? How and why?
Languages change over time. The youngsters bring new ways of using a language while elders often resist to change and stay close to traditions. The reasons why languages evolve are numerous but the most important ones are the following. First, the communicative needs such as distinguishing the singular and plural form of “you” by using expressions like “you guys”. The influence from other dialects has also brought the English language to change over time. British English often borrows expressions and sentence structures to American English. Moreover, as time goes by, languages tend to simplify themselves by using contractions and simpler structures. A hundred years ago, progressive verbs appeared and are gaining importance in the speech of English speakers.Plus, some mistakes are made by so many people that it becomes correct with time (data now used as an uncountable noun). Also, phonetically weak forms tend to disappear and to be replaced by to common form. Other changes have happened through time, for example, who has replaced whom, will has replaced the older expression shall and many others that you can find in the Practical English Usage book (Michael Swan).