Many verbs in English use a preposition to connect two parts of a sentence.
When we use a preposition with inform, it is not a phrasal verb, It is a prepositional phrase. The preposition modifies the verb depending on what you want to say.
The most common prepositions are of, about, on, and by.
When to use inform of
We use “inform of” when we want to show that one person tells the existence of some piece of information to another person. To inform somebody of something.
He informed me of his decision to leave the company.
I informed him of his options.
When you are a software engineer, you need to keep informed of current trends.
When to use inform about
Inform about is similar to inform of but it often implies that there are more details(more information) that we need to keep informed about.
Keep me informed about any decisions the company makes(of is also possible).
I informed the new employee about company policy(I went through the details with her).
This difference is also with the verb “to think”. To think of is usually used with the existence of a new idea whereas “to think about” is when you think longer about something.
When to use inform by
We use “inform” by when we use the passive voice and we want to include the agent(the person who does the action).
I was informed by my boss that I needed to arrive early.
He was informed by his neighbors.
When to use inform on
“Inform on” is usually used when we are giving incriminating evidence about someone. In this case, it is used in a similar way to “tell on”.
It is usually quite formal and mostly used in English writing and to do with matters with the police. It is not common when involving children misbehaving. In that case, tell on or tattle on, are more common
John informed on the gang to the police.
He had been recruited by the police to inform on his fellow gang members.
Peter told on me about the broken window.
Inform can also be used when we want to say that we have knowledge about a certain topic.
I am very informed on this matter.
Inform + no preposition
Inform is a transitive verb which means it takes a direct object similar to the verb “to like” You can’t say “I like…” without some object like a person or a thing. The verb “to inform” is the same. For this reason, we often use a preposition to connect the verb and the object(and the indirect object).
We don’t need a preposition when the information is implied(already known)
I informed Peter.
I informed Peter(about the trial).
Inform+ reflexive pronoun
As we discussed above, the verb “to inform” is a transitive verb so it needs an object.
If the subject and the object are the same then we need a reflexive pronoun.
I need to inform myself of the correct procedures.
You need to inform yourself of the correct procedures.
John needs to inform himself of the correct procedures.
We need to inform ourselves of the correct procedures.
They need to inform themselves of the correct procedures.