Re: Nominal or Adjectival ? advanced grammar level
Who steals my purse steals trash.
The short answer to your question is that it is both. This is a fused relative construction where the antecedent and the relative pronoun are fused together instead of being expressed separately as in simpler constructions. The underlined expression is thus a noun phrase whose head is fused with the first element of the relative clause.
"Who" is simultaneously head of the noun phrase and subject of the relative clause. The meaning is thus comparable to that of the non-fused The person who steals my purse steals trash.
In general, fused relatives with "who" just aren't used in contemporary English. In Shakespeare's time it was commonplace, as your example from Othello demonstrates, (in full: Who steals my purse steals trash; 'twas mine, 'tis his, and has been slave to thousands. It survived down to the 19th century. But it did not survive down to the present day.
It seems to be an isolated survival of an extinct construction type. Nowadays, we would use "whoever", so bear that in mind!
