“Love can't be pinned down by a definition, and it certainly can't be proved, anymore than anything else important in life can be proved.”

Appendix
The Causes of Evolution (1932)
Context: Unaided common sense may indicate an equilibrium, but rarely, if ever, tells us whether it is stable. If much of the investigation here summarised has only proved the obvious, the obvious is worth proving when this can be done. And if the relative importance of selection and mutation is obvious, it has certainly not always been recognised as such.

The Complete Neurotic's Notebook (1981), Unclassified

The Autocrat of the Breakfast Table (1858)

Enchantment (1999)

"Secret Love"
Poems Chiefly from Manuscript
Context: I hid my love in field and town
Till een the breeze would knock me down,
The bees seemed singing ballads oer,
The fly's bass turned a lion's roar;
And even silence found a tongue,
To haunt me all the summer long;
The riddle nature could not prove
Was nothing else but secret love.

Variant: It’s the tragedy of loving, you can’t love anything more than something you miss.
Source: Extremely Loud and Incredibly Close (2005), p. 208

Source: Closer

Source: The Kiss of Deception