Aquinas has written that ‘Concord is a union of wills, not of opinions’. This dictum is problematic because one would think that without some union of opinions, union of wills cannot be obtained. This chapter seeks to clarify the meaning of this dictum and to show that it does not imply that shared opinions are unnecessary for concord. It is argued that working behind Aquinas's dictum is his theory about love and what love does. The proper effect of love is to unite persons. Love unites them formally: the lover aims to resemble (participate in the form) of the beloved. The lover's movement toward resemblance involves a movement toward resemblance as to his acts of will.
Keywords: disagreement, friendship, beliefs, discord, heresy, lover, love