S'en falloir is a french third group verb. So, this verb is irregular and do not follow a regular conjugation pattern like first or second group verbs. Follow this link to see all the endings of the conjugation of most of the third group verbs :
conjugation rules and endings for the second group verbs.
Le verbe
« s'en falloir » is an impersonal verb. In linguistics, an impersonal verb is one that has no determinate subject. For example, in the sentence "It rains", rain is an impersonal verb and the pronoun it does not refer to anything. In many languages the verb takes a third person singular inflection and often appears with an expletive subject. In the active voice, impersonal verbs can be used to express operation of nature, mental distress, and acts with no reference to the do-er. Impersonal verbs are also called weather verbs because they frequently appear in the context of weather description. Common french impersonal verbs:
pleuvoir =>
« il pleut »,
grêler =>
« il grêle »,
falloir =>
« il faut »,
s'agir =>
« il s'agit »,
advenir =>
« il advient ».
The verb
s'en falloir is the reflexive form of verb
falloir. In grammar, a reflexive verb is, loosely, a verb whose direct object is the same as its subject, for example, "I wash myself". More generally, a reflexive verb has the same semantic agent and patient (typically represented syntactically by the subject and the direct object) are the same. For example, the English verb to perjure is reflexive, since one can only perjure oneself. In a wider sense, the term refers to any verb form whose grammatical object is a reflexive pronoun, regardless of semantics; such verbs are also referred to as pronominal verbs, especially in grammars of the Romance languages. A reflexive verb is always conjugated with a reflexive pronoun. Here is the list of the french reflexive pronouns:
« me »,
« te »,
« se »,
« nous »,
« vous »,
« se ».
