Passionate love, "a state of intense longing for union with another. Reciprocated love (union with the other) is associated with fulfillment and ecstasy; unrequited love (separation) is associated with emptiness, anxiety, or despair."[1][3]
Companionate love, "the affection we feel for those with whom our lives are deeply entwined."[1][3]
Companionate love is commonly called "attachment"[7][10][6] (sometimes in relation to attachment theory,[11] but not all authors agree)[4] or compared to strong liking,[4] friendship love[4] or Storge.[4]
Passionate love feelings are most commonly measured with a psychometric instrument (a questionnaire) called the Passionate Love Scale (PLS);[12] however, a study by Sandra Langeslag and colleagues found that the PLS has some questions which measure companionate love.[8] This led the team to develop the Infatuation and Attachment Scales (IAS), measuring what they call:[8]
Infatuation (similar to passionate love), "the overwhelming, amorous feeling for one individual that is typically most intense during the early stage of love (i.e., when individuals are not (yet) in a relationship with their beloved or are in a new relationship)."[10]
Attachment (similar to companionate love), "the comforting feeling of emotional bonding with another individual that takes some time to develop, often in the context of a romantic relationship."[10]
The IAS is designed for more refined measurements than the PLS,[8] but infatuation and attachment can otherwise be considered synonymous as a concept with passionate and companionate love.[8][10]
Evolutionary theories of passionate and companionate love suggest these two types of love exist for different purposes and thus follow different mechanics.[5][6] Passionate love is said to usually only be present in the early stage of a relationship[7] with companionate love often following after;[2][9] however, in a phenomenon called long-term romantic love, intense attraction can remain much longer than is typical for passionate love, but without obsessional elements.[13][14]
Both passionate and companionate love contribute to relationship satisfaction.[4][13] Passionate love is associated more with satisfaction in the early stage of a relationship.[13] Companionate love is associated with satisfaction in the long-term more than the short-term.[13]
Passionate and companionate love can also be further distinguished from a third important type of love, compassionate love, which is love focused on caring about others.[4]