Hello!
I work in an IT company, I have a problem of how to express the idea (from correspondence with the customer) “The program must/should work” means we improved all the bugs and now we are almost sure that it will work.
Which of the modal verbs is better here – must or should? Or maybe it is usually expressed in some other way?
In Grammar by I.P.Krylova (rus.) there is a meaning of “must” as follows “Supposition implying strong probability”, does it suit here?
In Murphy Grammar:
We use “must” to say that we feel sure something is true.
We use “should” to say that we expect something to happen.
“the program should work” is correct, meaning that you expect it to work. However, in a formal business situation this may sound a bit casual and vague, and in that case it may be better to say something like “we believe that the program is now working correctly”.
“must” is wrong here.
By the way, saying that you have “improved” the bugs doesn’t sound great (like the bugs still exist but just aren’t quite so bad). If the bugs no longer exist then you should say you have “fixed” the bugs.