If current trends prevail, the marriage rate in America will fall to zero by 2042. Still, when presented with such speculation, the mind drifts easily away from self-inspection toward matters of fact. The decline in marriage, some say, mirrors the decline in religious belief and its attendant institutions. Others suggests that millennials, the largest living generation, are merely waiting for better conditions to tie the knot. Another indisputable graph tells us that the rate of marriage in the 20th century is linked in some way to world wars and financial crises. We rush to marry before the war and after — it’s hard to kill and wed at the same time. And when depressions and recessions inevitably strike, we avoid the altar: we don’t say I do; or we say I don’t.