Non-native speakers of English are not the only ones who regularly confuse these words or use them incorrectly. Unfortunately, native speakers are equally guilty of mistakes.

Here’s how to use them correctly:

• “compose” – to make up, i.e. the parts compose the whole
• “be composed of” – to be made up of, i.e. the whole is composed of its parts
• “composes of” – INCORRECT

• “comprise” – to be made up of, i.e. the whole comprises its parts (opposite to “compose”)
• “be comprised of” – INCORRECT, but commonly used by native speakers to have the same meaning as “consist of” and “be composed of”
• “comprises of” – INCORRECT

Here are some examples of usage:

• 24 lawyers, including 6 partners, compose the Energy Department.
• A hallway, living room, two bedrooms, a kitchen, bathroom and separate WC compose the apartment.
• 28 member states compose the European Union.

The above examples, although technically correct, would sound a little strange to a native English speaker. It would be better to write the following:

• The Energy Department is composed of  24 lawyers, including 6 partners.
• The apartment is composed of a hallway, living room, two bedrooms, a kitchen, bathroom and separate WC.
• The European Union is composed of 28 member states.

In the above examples “consists of” would work as well as “is composed of”. Alternatively you can use “comprise”:

• The Energy Department comprises  24 lawyers, including 6 partners.
• The apartment comprises a hallway, living room, two bedrooms, a kitchen, bathroom and separate WC.
• The European Union comprises 28 member states.

Remember the whole comprises the parts and the parts compose the whole. So avoid this common mistake:

• 28 member states comprise the European Union.

I also sometimes see “comprise” used when the writer should use “include” or “contain”.

WRONG
Please note that a special non-liability clause is comprised in the Lease.
RIGHT
Please note that the lease contains / includes a special non-liability clause.
WRONG
The installation was not comprised in the Council of Ministers’ Regulation.
RIGHT
The installation was not included in the Council of Ministers’ Regulation.

Remember that “comprise” has an exhaustive meaning, i.e. it refers to all the parts.

• The apartment comprises a hallway, living room, two bedrooms, a kitchen, bathroom and separate WC.

In the above example the list of rooms is complete. There are no more rooms in the apartment.

“Include” or “contain”, on the other hand, are not exhaustive, i.e. they do not refer to all the parts.

• The apartment includes a hallway, living room, two bedrooms, a kitchen, bathroom and separate WC.

In this example the apartment may contain more rooms.