English has a number of modal verbs which generally do not inflect (most of them are surviving preterite-present verbs), and so have only a single form, used as a finite verb with subjects of all persons and numbers. These verbs are "can" and "could", "may" and "might", "shall" and "should", "will" and "would", as well as "must", "ought (to)", "need" and "dare" (when used with a bare infinitive), and in some analyses "used (to)" and "had better". (The modals "could", "might", "should" and "would" are historically the past tense forms of "can", "may", "shall" and "will" respectively, though they are not always used as such.) These verbs do not have infinitive, imperative or participle forms, although in some cases there exists a synonymous phrase that can be used to produce such forms, such as "be able to" in the case of "can" and "could". The negation of "can" is spelled as a single word, "cannot". There are contracted forms " 'll" and " 'd" for "will" and "would" (in some cases possibly from "shall" and "should").