Hatfield and Walster's (1981) Three-Factor Theory suggests that in order for an individual to fall in love, one must be:
  1. From a cultural background in which we learn about love and expects it to happen.
  2. In the presence of an "appropriate" love object (in terms of gender, age, attractiveness, etc).
  3. Physiologically aroused. This is interpreted an labelled as "love" or "attraction".
In other words what Hatfield and Walster is stating is that:
Love-Oriented Culture + Love Object + Arousal = Love