(Dilbilim) In linguistics, a protasis is the subordinate clause (the if-clause) in a conditional sentence. For example, in "if X, then Y", the protasis is "if X". The other clause ("then Y") is called the apodosis
A subordinate clause is a clause in a sentence which adds to or completes the information given in the main clause. It cannot usually stand alone as a sentence. Compare main clause. a dependent clause