Some of you are saying, "Formal Methods is ...? What's wrong with these people, ain't nobody learned them no grammar!" In an age in which few people care about the proper use of language, your concern is commendable; however, in this instance, your concern is also unwarranted.
In these pages, we are using the term formal methods to refer to a particular collection of knowledge. Just as the plural-sounding term fluid dynamics is treated as singular, so too may the term formal methods be treated as singular. A legitimate argument can be made as to the acceptability of treating the term as plural, but no legitimate argument can be made as to the necessity of doing so.