... modal verbs can , could , may , have to ” “ ” “ ” “ ” and must “ ” in different contexts. 3.2 Implications for teaching English modal verbs can, could, may, have to, and must to Vietnamese secondary ... modal verbs can, could, may, have to and must . An analysis specializing in errors in using English modal verb will bring about a number of benefits. First, it will tell a teacher of English how ... many Vietnamese students had problems in understanding and using modal verbs can , could ,“ ” “ ” may , have to ” “ ” and must ”. A large number of errors could be traced to the following...