Frequent in American English and British English is the use of “ought” without "to" in questions and negations: “He ought not do that”.
Modal "would" is used in if-clauses when it indicates willingness, e.g. If you would agree, everything would be fine. But American English extends the use of "would" to if-clauses where no volition is involved, e.g. If it wouldn't rain everything would be nice. Expression “’d rather” which is a contraction of “would rather” sometimes turns into had rather (chiefly in AmE).
"Shall" is fixed in American English almost only to questions inquiring about the desirability of the speaker’s doing something, e.g. Shall I get you a cup? But more common are Would you like... ? Should I... ? Can I?
“Must” is losing its ground to "have to" or "have got to" in its obligation meaning in American English.
The subjunctive is more common in AmE than in BrE. Typically American usage is called mandative subjunctive and it is used after the predicates of command and recommendation and some other predicates that mark desirable future action:
e.g. We suggest that you be on time tomorrow. It is important that you not misunderstand me.
While this is somewhat formal usage in AmE it is by no means unusual in the everyday language. In BrE, on the contrary, it is largely restricted to formal written usage. What BrE uses in its place is either putative should (e.g. It is mandatory that you should not misunderstand me), which is also available in AmE, or the indicative (e.g. It is mandatory that you don’t misunderstand me).
The Perfect Tenses. The use of Perfect is interpreted somewhat differently in the two varieties. While there is basic agreement, American English speakers can choose to use the Past Indefinite in the sentences with "just", “yet”, “already", e.g. He just came.
Tag questions are common both in American English and British English. But American English seems to prefer the non-grammatical type, e.g. I'll return tomorrow, right/O’kay?
1.8.2. Differences in the Noun and Pronoun
Collective nouns government, team, committee are singular in American English. American English has plural for accommodations, sports where British English has abstract and non-countable accommodation, sport. In British English they use fish – fishes, shrimp – shrimps but plural is impossible in American English. BrE has the plural overheads and maths where AmE has singular overhead, math. In American English committee, council correlate with the relative pronoun "which".
e.g. BrE the Committee who are considering….
AmE the Committee which is considering.
In Southern AmE "you all" and the possessive "you all's” is widespread. It denotes second person plural (y'all). Although such pronoun as youse has the relative acceptance of you all. Traditionally, AmE uses indefinite pronouns one on the first reference, but uses he / his / him as appropriate to continue the reference.
Let’s have a closer look at this example: e.g. One tends to find himself/herself in agreement in order to maintain his or her self-respect. American English speakers find the use of masculine form needlessly sexist. British usually use: oneself and one’s.