CONFUSING THAT (RP) & THAT (SC)

THAT can be a little confusing due to the fact that there is a THAT used for subordination (subordinating conjunction) and another, which is the relative pronoun.

THAT as a subordinating conjunction does not usually follow a noun; therefore it does not modify one. If THAT does not follow a noun, chances are it is a subordinating conjunction and not a relative pronoun.

e.g. I THOUGHT THAT YOU HAD LEFT.
- There is no noun preceding THAT, therefore it is a subordinating conjunction.

Another way is to check if THAT is a relative pronoun or a subordinating conjunction is to verify if the clause following THAT can be used as an independent clause (excluding THAT, of course).

e.g. I THOUGHT THAT YOU HAD LEFT.
- “You had left” can be an independent clause (excluding THAT); therefore, THAT is a subordinating conjunction.

Yet another way to check if THAT is a relative pronoun or a subordinating conjunction is to verify if the word THAT can be exchanged for the word WHICH.

e.g. I HAVE NEVER EATEN MEAT THAT WAS SO TENDER.
- I have never eaten meat WHICH* was so tender.

*NB: This is merely to check if THAT is a relative pronoun. It is not recommended for the sentence itself.