For me, the distinction between primary and secondary substance is an important one. Primary substance is about particular referents or objects. We may also think of primary substance as being undifferentiated tokens rather than classified or categorised tokens. Secondary substances are categorised types of tokens.
The symbol given to a primary substance is unique within a context. The symbol given to a secondary substance is not unique within a context.
Primary substances are without properties. Secondary substances are with properties.
The properties of a primary substance do not define the named primary substance. The properties of a secondary substance do define the named secondary substance.
The term of a primary substance is without meaning.