Hi Iris ESL course books don't (tend to) study phrasal verbs in grammatical detail, grouping both preposition verbs and particle verbs within the 'phrasal verb' group, which means you don't have all the information to make decisions like this. As Amul pointed out, you also need to know whether or not the phrasal verb is transitive, and that's why your textbook suggests you use a dictionary. I know that not all dictionaries make this clear, but there are quite a few that provide (alphabetical) lists, for example: http://www.englishpage.com/prepositions/phrasaldictionary.html If you really want to study these in more detail, Wikipedia provides quite a good explanation: http://en.wikipedia.org/wiki/Phrasal_verb. HTH Rachel

I've tried to work out if there is a magic pattern or not, and unfortunately there doesn't seem to be one. You just have to learn them as you go.

Thank you.It would be easier if dictionaries gave this information.

I am not sure about this, but just thinking about a few phrasal verbs, I get the impression that those that don't take a direct object are definitely not separable. Those that do take a direct object can be separable, but need not be. As I said I am not sure, and it is probably best to follow Peachey's advice and learn them individually as you go along.