Sentence structure : comma + adjective problem

Question

These make up the entire content of the mind, and Herbart saw them not as static but dynamic elements, able to move and interact with one another.

I could not understand exactly how the "able to move and interact with one another" part can appear without a relative pronoun. It seems that the part modifies or tells more about the previous clause.

Does a comma function just as a relative pronoun? Also, if there's an omission between the comma and "able to move ~," what is it? I would like to know the grammar structure of the above sentence. Thank you in advance.

Answer 1

Adjective phrases are suitable as reduced adjunct clauses. You could view it as a non-restrictive relative clause: "..., which are able to ..."