Courses hand you two lists of phrasal verbs: the separable ones, whose object can sit inside the verb, and the inseparable ones, whose object cannot. Then they tell you to memorise which verb belongs to which list, as though this were vocabulary. It is not vocabulary. The two lists are two different structures wearing identical clothes, and a single test tells them apart in about a second.
What follows is that test, worked examples of both kinds, and the thing the lists in your textbook cannot show you: why the same verb sometimes prefers one order and sometimes the other. Understand the difference in structure and you will not need the lists again.
What a phrasal verb is, and why there are two lists
A phrasal verb is a verb combined with one or two small words, where the combination works as a single verb and usually carries a meaning you could not work out from the parts on their own. That is the whole difficulty of them: the grammar is ordinary, but the meaning is not. English has several thousand, and they do most of the everyday work that a single formal verb does in careful writing.
Only some of them raise a question of word order at all. A phrasal verb that takes an object is transitive, and only transitive ones can be separable or inseparable. Many phrasal verbs are intransitive: they take no object, so nothing could sit in the middle even in principle.
The car broke down on the motorway.
She grew up in Manchester.
The plane took off an hour late.
None of the three lines above could be split, because there is no object to place anywhere. So the first question to ask about any phrasal verb is whether it takes an object at all. If it does not, there is no word-order problem to solve, and neither of the two lists applies to it.
Two structures, one appearance
The small word at the end of a two-part verb is one of two very different things. It is either a particle, which belongs to the verb and can move around the object, or a preposition, which belongs to the noun after it and cannot be separated from it. A preposition is glued to whatever follows; a particle is not glued to anything. That single structural difference is the whole of what separable and inseparable mean.
Turn off the radio.
Turn the radio off.
Turn it off.
I ran into my old teacher.
I ran into her.
In the first group the object moves freely to either side of the small word. In the second group nothing moves at all. Here is the test that separates them without any memorising: swap the object for a pronoun and try to place that pronoun in the middle. If it fits there, you have a particle and the verb is separable. If the pronoun refuses the middle and has to follow the small word, as it does in the last line of the second group, you have a preposition and that verb is inseparable.
There is a second clue for your ear. In neutral speech a particle carries stress and a preposition usually does not, so the two groups sound different even when they look the same on the page.
With a pronoun, the middle is not a choice
This is the part most courses bury, and it is the most useful thing here. Textbooks present the middle position as an option, and with an ordinary noun object it genuinely is one: the first two lines of the first group above are equally natural. With a pronoun it is not an option. A splitting verb requires its pronoun object in the middle, which is why the third line of the first group is the only possible form there. Heavy contrastive emphasis can bend this in speech, but that is a special effect, not a position you should be reaching for.
Learners who treat the position as free end up producing a word order that fluent speakers simply do not use, and because pronouns are everywhere, the error repeats in almost every sentence. Fixing this one habit does more for how natural you sound than learning another twenty of these verbs.
Separable phrasal verbs: ten worked examples
The ten numbered lines below collect some of the most common separable phrasal verbs in English, each one shown with its object already sitting in the middle. Every object here is an ordinary noun phrase, and every line is a sentence you could use today.
1. Please fill this form in before Friday.
2. She called the meeting off an hour before it started.
3. Could you pick the children up at four?
4. Write the address down before you forget it.
5. They threw the old sofa away.
6. I looked the new word up in a dictionary.
7. Switch the lights off when you leave.
8. He handed his notice in on Monday.
9. We put the decision off until March.
10. The teacher gave the exam papers out.
Every one of the ten lines above is equally correct with the object moved to the end, after the small word. That is precisely what separable means: both positions are available, and with a noun object neither one is more correct than the other. Replace any of those objects with a pronoun, though, and only the middle position survives, which is where you will spend most of your time, since pronouns are far more frequent in real speech than full noun phrases are. Notice too how short every object in the group is: length decides which of the two orders sounds better, as the section below explains.
Inseparable phrasal verbs: the ones that never split
The question learners ask most often is which phrasal verbs cannot be separated. The honest answer is not a list to memorise but a structure to recognise: where the small word is a preposition, the object must follow it, and no exception is coming.
1. We came across an old photograph in the attic.
2. She looks after her neighbour’s cat every summer.
3. The committee looked into the complaint.
4. He takes after his mother.
5. They are dealing with the problem this week.
6. She got over the illness slowly.
7. I am waiting for the examination results.
8. The report calls for a change in the law.
In all eight lines above the object sits directly after the small word, and it stays there when you swap it for a pronoun. There is no middle position to argue about. These verbs take an object all the same; they simply refuse to let anything come between the verb and the preposition. Put the object in the middle of any of the eight and the result is not merely unusual English; it is not English at all.
Compare the two numbered groups and the difference stops being a matter of memory. The first takes a particle, so the object may go on either side of it. The second takes a preposition, so the object has exactly one place to be. Everything else about separable and inseparable phrasal verbs follows from that one contrast.
Weight decides the rest
Even when splitting is allowed, it is not always the better choice. What decides it is how heavy the object is.
She turned off the light.
She turned the light off.
She turned off every light on the ground floor of the freezing old house.
The first two lines above are short, and either arrangement sounds fine. The third carries a long object with modifiers trailing behind it, and splitting the verb around all of that would leave the listener holding an unfinished verb for a dozen words before the small word finally arrives. So the same verb, with no change in its grammar, prefers different orders depending on the weight of what follows. This is why real usage sometimes contradicts the lists you were given, and why a rule about structure serves you better than a rule about individual verbs.
Three-word verbs settle it for you
Some of these verbs come with a third element, and those are the easiest of all.
I am looking forward to it.
She puts up with a lot.
The last element in each of the two lines above is a preposition, so the object always comes at the very end, pronoun or not. Nothing ever goes in the middle. One more warning: the same pair of words can be a splitting combination with one meaning and a non-splitting one with another, so the question is never really about the verb as a dictionary item. Run the pronoun test on the sentence in front of you and it will answer for that sentence.
Register: when a single-word verb is the better choice
Phrasal verbs dominate speech and informal writing. In an examination essay or a formal report, many of them have a single-word equivalent that lifts the register, and choosing between the two is a separate skill from placing the object correctly. Getting the word order right is not the same as deciding that this was the right verb for the context. The reference page pairing these verbs with their single-word formal twins sets the two columns side by side, which is the quickest way to see what a piece of writing gains and loses by the swap.
How to learn phrasal verbs without memorising two lists
The lists in most books run to several hundred entries, and very few learners reach the end of one. A better use of your time is to learn each new phrasal verb inside a complete sentence with its object already in place, so that the word order arrives attached to the meaning instead of as a separate rule to recall later. When you meet an unfamiliar one, ask three questions: does it take an object at all; if it does, can a pronoun sit in the middle; and does the combination mean something the separate words do not.
Then produce them. Recognising a phrasal verb on a page is easy and using it correctly under time pressure is hard, so an exercise that forces you to place the object yourself is worth more than any amount of reading about the rule. That is the gap the practice set linked below is built to close.
Where to take this next
The lesson on where the small word goes in a two-part verb sets out the pattern with more cases, and the practice set that drills pronoun placement is the one to repeat until the middle position stops feeling like a decision. For a single verb that generates dozens of these combinations, the reference page that collects them is worth a slow read, and the entry for the two-part verb meaning to leave something for a later time shows how one of them behaves in real sentences. The entry for the item meaning to produce an idea, a plan or an answer is a useful second example of how one of these behaves once you meet it in a sentence.