The term 'substance' is used in two ways.
First substance is any individual thing that exists in itself. You, dear reader, are an example of first substance. You are an individual, particular man.1
Second substance is the nature of some group of individual things that exists in themselves taken as the species of all things that share said nature. The use of the word 'man' to mean the species of you6, me and every other rational animal on dear old Terra is an example of second substance.7
 Certainly in the unmarked sense, possibly in the marked sense as well.2
 If you are not a man in either sense, dear reader, please inform me of this. I would be extremely pleased to be the person to make "first contact" with another sapient3 species. Unless of course you wanted to eat me. That would be really uncool.4
 'Sapient' is a superior word to 'sentient', since 'sentient' literally means "capable of sensation," which is true of all animals. 'Sapient', on the other hand, literally means "capable of wisdom," something true only of rational animals.
 I feel that I must point out, dear reader--out of the sense of duty I feel towards the spiritual work of mercy that is instructing the ignorant--that eating a fellow sapient being would be immoral.5
 If you already knew this but just don't care, then consider this an example of admonishing the sinner instead.
 Again, unless your not.
 See previous notes. I suppose, dear reader, that if you aren't human we will either be forced to say that 'man' and 'human' are not interchangeable, but instead say that 'human' us a subset of 'man'; or we will be forced to redefine 'man' as "rational animal of the species homo sapiens" and apply the definition "rational animal" to some other word.8
 Yes, I am aware that this post is over 50% footnotes.