• Here are some examples:
grow up: Jane grew up in India, but she moved to Canada after graduation from university.
take off: Harry’s plane took off at noon after a long delay.
turn up: Jill was surprised but pleased when Tom turned up half an hour early.
back down: Dick first refused to do the job, but he backed down when Harry threatened to fire him.
catch on: At first, Sarah didn’t understand what Harry was doing, but she soon caught on.
die out: Tom explained to his students that the practice of foot binding had died out nearly a hundread years earlier.
slip up: Jill usually does an excellent job of organizing Harry’s appointments, but recently she’s slipped up a few times.
• Since they have no objects of any kind, intransitive phrasal verbs do not exhibit the characteristic of “separability.” Their identity as phrasal verbs is established by the fact that they are verb-particle combinations which have unitary meanings. Like other types of phrasal verb, they exhibit varying degrees of idiomaticity and informality.
• There is no difficulty in distinguishing between intransitive phrasal verbs and prepositional verbs (as there can be in the case of transitive phrasal verbs) since all prepositional verbs have prepositional objects. There is however a possibiity of confusion between intransitive phrasal verbs and “free combinations” of verb + adverbial particle. For example, in the sentence When Jill called, Jack ran up, “up” is an adverbial indicating the direction in which Jack ran. By contrast in the sentence, When Jill called, Jack freaked out, the particle “out” is a part of the intransitive phrasal verb “freak out” (meaning “to become very upset or afraid.”)
• Notice that of the seven examples given above, one, “take off,” does not allow for single-word substitution. It could be replaced only by another multi-word item such as “become airborne” or “take flight” or by a paraphrase such as “leave the ground”. Plausible substitutions are available for the others: “mature” for “grow up,” “arrive” for “turn up,” “relent” for “back down,” “understand” for “catch on,” “disappear” for “die out,” “err” for “slip up.” Of these, however, only “arrive” and “disappear” are fully satisfactory, and they cannot be regarded as synonyms because both these phrasal verbs are have other senses for which the same substitution could not be made. The other substitutions would almost certainly never be used by a native speaker except, perhaps in the course of trying to explain one of the phrasal verbs to an ESL student. And even in that situation it should be kept in mind that contemplating the substitutions only serves to emphasize the semantic distinctness (and therefore the semantic value) of phrasal verbs.