Are primary, secondary, and tertiary amines considered functional group or chain isomers?

Consider $\ce{C3H7NH2}$. Can one make $3$ different isomers with this molecular formula? My question is that are they functional group isomers or chain isomers?

I have been told that they are functional group isomers but I intuitively think that they are chain isomers.

• I can make four different isomers of this. – Ivan Neretin Nov 3 '15 at 12:50
• Yes I know we can , but my question is are they functional group or chain ? – Akshay Pratap Singh Nov 3 '15 at 13:08