It does make a difference if we have God's Word - particularly about Jesus' life and death - to teach us what love means in practice. Paul explained that husbands should love their wives as Christ loved His people: Christ poured out everything He had and was for us, and that, says Paul, is the model for our love too. But it's not just a matter of abstract teachings. Christians have believed that there's also supernatural power in God's Spirit to help us follow that model through; in creativity, mutual forgiveness, perseverance, devotion.

But suppose all that is gone: how can we know what it really means to love? "Love means never having to say you're sorry" (Love Story) is self-evidently stupid. But is love maybe a bargain where both partners receive care and fulfilment? Possibly; but then what happens when the fulfilment doesn't materialise?