Some words that look like prepositions do not always function as prepositions. Consider the following two sentences:

The balloon rose off the ground.

The plane took off without difficulty.

In the first sentence, off is a preposition that introduces the prepositional phrase off the ground. In the second, off does not function as a preposition. Instead, it combines with took to form a two-word verb with its own meaning. Such a verb is called a phrasal verb, and the word off, when used this way, is called an adverbial particle. Many prepositions can function as particles to form phrasal verbs.

Phrasal verbs

The verb + particle combination that makes up a phrasal verb is a single entity that often cannot be torn apart.

However, when a phrasal verb takes a direct object, the particle may sometimes be separated from the verb by the object.

I picked up my baggage at the terminal.

I picked my baggage up at the terminal.

If a personal pronoun (such as it, her, or him) is used as the direct object, that pronoun must separate the verb from its particle.

I picked it up at the terminal.

Prepositional verbs

Some idiomatic two-word verbs are not phrasal verbs.

We ran into our neighbor on the train.

Here, into is a preposition, and our neighbor is its object. You can’t separate the verb from the preposition (We ran our neighbor into on the train does not make sense in English). Verbs like run into are called prepositional verbs.

Notice that run into our neighbor is different from a normal verb and prepositional phrase, such as run into a room. The combination run + into has a special meaning, “meet by chance,” that you could not guess from the meanings of run and into.

English has many idiomatic prepositional verbs. Here is a small sample.

Other prepositional verbs have predictable meanings but require you to use a particular preposition that you should learn along with the verb: depend on, look at, listen to, approve of.

Finally, look out for phrasal-prepositional verbs such as these, which include a verb, a particle, and a preposition in a set order.