To be formal and absolutely "correct", one should write in British English:
If you have any questions, I shall be happy to answer them.If one were to write:If you have any questions, I will be happy to answer themthen that would mean that the speaker is willing or intends or promises to be happy, on condition that any questions are presented to him by his correspondent. Consider the following
I should be pleased if you would reply to my enquiry at your earliest convenience.
The reasoning behind the use of should in the 1st person is that if one writes: "I would be pleased...", then the would indicates that the speaker in the 1st person is hypothetically willing to be pleased; that the speaker hypothetically intends or tentatively promises to be pleased.
However, when there is no volition (willingness or intention) on the speaker's part to be pleased, then the speaker is merely indicating that if the other party were hypothetically willing to do something, then that would oblige the speaker to be pleased, which obligation in the first person is expressed by the modal auxiliary verb shall in its subjunctive mood, namely should.
If the speaker does not wish to express a hypothesis or, as the case may be, does not wish to use a formal, polite register by using the subjunctive mood of the verbs will or shall, namely would or should respectively, then the formula is:
I shall be pleased if you will...
However, in spoken English, the modal auxiliary verbs would and should in the subjunctive mood are both shortened to " 'd ", hence:
I'd be pleased if you'd...
Likewise, in declarative statements will and shall are almost invariably shortened in spoken English to " 'll ".
This shortening of the modal verb forms leads to the erroneous belief that " 'll " always means "will" and that " 'd " always means "would".
This error is further compounded by the constant refrain that nobody says "shall": that is not true.
In the United States, few people say "shall" now, but it is still used in American legal English to express an obligation or a rule, but not an absolute duty (must), passed on by the speaker to another party, e.g:
A meeting shall take place every month.
However, in both American and non-American English, should has the far more common function of expressing advisability, e.g:
A meeting should take place every month.
It is this more common function of should that makes many people think that "should" always means advisability: it does not. When a speaker says:
I should be pleased if you would reply to my enquiry at your earliest convenience...
he is politely and formally saying that it would be incumbent upon him to be pleased if something were done, namely an obligation would be imposed upon him by another party's action.
I should also like to add that up to at least the early 1950s Americans were taught to use shall/will and should/would in the way that I have described above. However, as a result of both the more informal nature of spoken English and its ever increasing use worldwide as a lingua franca, I should think that the majority of people that speak English as either a mother tongue or a second language, say "would" instead of "should" or, which is the more likely case, "'d" in the first person, and only use "shall" when asking questions in the first person.
Some may argue that the system described above is an example of prescriptive grammar. However, I regularly see and hear "shall" and "should", used in the way described above, in British English and also not too infrequently in American English. Only last week (June 16th 2010) I received a letter from a British consulate, that stated:
We shall inform you if there are any delays in processing your passport application.
The consulate was not promising me anything: the consulate was simply stating its obligation to me if any delays took place.
I should therefore argue that those who categorically state that the above use of "shall" and "should" is somehow wrong or "old fashioned" are the real prescriptivists.
