Our politicians have been pandering again. This demotivates the voters. – Entire first sentence as antecedent
When we take the bolded sentence away from its antecedent, where does that leave it grammatically both in and outside of the structure.
This is the subject of the second sentence but obviously without it’s antecedent doesn’t make sense alone. But is it classed as independent when paired with it’s antecedent and dependent when alone ?
The antecendent of “this” is “pandering”. Grammatically the second sentence is “independent”. It is an independent finite clause, and it is not subordinate to any other clause. An independent clause can contain pronouns, and these pronouns may have antecedents that are outside the clause. This does not make the clause dependent. Compare:
It sat on the mat. (Independent finite clause, and a complete sentence.)
that sat on the mat (could be a subordinate relative clause, not independent)
if it sat on the mat (Subordinate clause, with a subordinating conjuction “if”)
So “Independent” does not mean “all pronouns refer to something in the same sentence”. It means the clause is grammatically complete, as in the first example, but no the others.
“This demotivates the voters.” (an example of an independent clause, and a complete sentence)
Removing the antecedent leaves a grammatical utterance but one that is semantically rather vacant. — Tᴚoɯɐuo