| behooves(must, should, requires, behoves) |
| have to(verb, expression, must, should, requires) |
| is becoming(verb, expression, must, should, requires) |
| is logical(verb, expression, must, should, requires) |
| is natural(verb, expression, must, should, requires) |
| is necessary(verb, expression, must, should, requires) |
| is reasonable(verb, expression, must, should, requires) |
| is responsible for(verb, expression, idiom, must, should) |
| must(should, behoves) |
| ought to(verb, expression, must, should) |
| requires(must, should, behoves) |
| be duty-bound to(must, should) |
| be expected(have, behoove, beseem) |
| be fitting(have, behoove, beseem) |
| be incumbent upon(have, behoove, beseem) |
| be necessary(have, beseem) |
| be needful(have, behoove, beseem) |
| be required(have, behoove, beseem) |
| be requisite(have, behoove, beseem) |
| be right(have, behoove, beseem) |