Answer:
It establishes a condition for the action in the independent clause.
Step-by-step explanation:
A subordinate clause (also called dependent clause) is a clause that, unlike an independent clause, can't stand alone as a complete sentence. It provides additional information about the content of the independent clause it's connected to by a subordinating conjunction. One of many subordinating conjunctions is if, and it's used to establish a condition for the action in the independent clause:
- If you wouldn't say it to a friend - condition (subordinate clause)
- Find something more reasonable to say to yourself - the action that should be realized if the condition is fulfilled (independent clause)