Wittgenstein contrived to quarrel, not only with Frank, but also with Lydia. Some years later she remembered the incident in a letter to Keynes. ‘What a beautiful tree’, she had remarked. Wittgenstein glared at her and asked, ‘What do you mean?’ so fiercely that she burst into tears.

The degrees of intensity are often more accurately described as degrees of saturation (of an experience with pleasantness) that are characteristic of the experience in question. Lust, for instance, is so highly saturated with pleasantness that is has usurped its very name.