In classical philosophy, dialectic (Greek: διαλεκτική) is an exchange of propositions (theses) and counter-propositions (antitheses) resulting in a synthesis of the opposing assertions, or at least a qualitative transformation in the direction of the dialogue. It is one of the three original liberal arts collectively known as the trivium (the other members are rhetoric and grammar). In ancient and medieval times, both rhetoric and dialectic were understood to aim at being persuasive (through dialogue). The aim of the dialectical method, often known as dialectic or dialectics, is to try to resolve the disagreement through rational discussion. One way — the Socratic method — is to show that a given hypothesis (with other admissions) leads to a contradiction; thus, forcing the withdrawal of the hypothesis as a candidate for truth (see also reductio ad absurdum). Another way of trying to resolve a disagreement is by denying some presupposition of the contending thesis and antithesis; thereby moving to a third (syn)thesis or "sublation".