All cats in the dark are grey

This of course is true, as far as human perception is concerned. It’s probably not that cats turn grey in the dark although of course they might; we are never going to know one way or the other. It’s like that old thing about the Tree in the Quad – the philosophical argument put forward by Bishop Berkeley:

  • There was a young man who said \God
  • Must think it exceedingly odd
  • If He finds that the tree
  • Continues to be,
  • When there’s no one about in the Quad.

This doctrine is known as Phenomenalism, and Phenominalists would claim that only such things as we perceive with our senses from one moment to the next can be said to exist. So, when we are not looking at the tree, the tree isn’t there. This is manifest nonsense, or at least impractical. Are trees scattering in all directions as we whisk ourselves away, only to re-plant themselves the minute we whisk ourselves back? Or might they be more sophisticated, materialising and de-materialising themselves in a nanosecond like leafy Tardis-is-is-es (Tardisii?)?

Ergo, if in the middle of the night my cat William jumps on the bed, miaows and appears to me to be grey, how do I nevertheless know that he’s a vivid shade of ginger? He may be in fact be grey only for as long as I’m looking at him. The minute I look away – back to ginger. If, like chameleons, cats can change colour at will, I imagine it amuses them greatly to do so. Excellent game!

Of course I could tell it was William with my eyes shut. He’s twice the size of all the other cats and weighs several tons more.

It’s just a saying, really. Attributed to Benjamin Franklin, it was rumoured to be his witty, if sexist and unpleasant way of explaining why it’s perfectly all right to take an older lady to bed. However, the saying goes back much further than that. In 1546 it appeared in John Heywood’s book of proverbs as When all candles be out, all cats be grey, which probably meant something less specific: that physical appearance is the least important thing about a person; it’s what’s inside that counts.

But why are all cats grey in the dark?

 This is the Science Bit and I’m no scientist so I’ll make it as pain-free as possible. It’s due to something called the Purkinje effect or Purkinje shift (after the Czech anatomist Jan Evangelista Purkyně). This is ‘the tendency for the peak luminance sensitivity of the eye to shift towards the blue end of the spectrum at low illuminance levels’. In other words a flower that appears bright red in full daylight fades to a darker, duller red at dusk and to black or grey at night. This goes back to those rods and cones inside our retinas (remember rods and cones from school biology? No, rods and cones, not rods, poles or perches…). The cones are very sensitive to colours and give us excellent vision in the daylight; the rods are very sensitive to light, but not to colours, and it is the rods we use to see whatever we can still see in the dark. This is why in moonlight, for instance, human beings become virtually colour-blind. It’s also why submarines are kept dimly lit, to preserve the night-vision of crew members, and why aeroplane cockpits use red lighting so that the pilots can both read the instruments and see outside the cockpit…

…and why cats appear grey. Which begs one further question:

If a cat in the dark is grey to me, what colour might I be to a cat?

Neither cats nor humans can see in pitch darkness. Cats can see considerably better than humans because they have eyes adapted to evening hunting expeditions. A cat has very large eyes in relation to the size of his head, and he can open his irises wide to let in as much light as possible. Cats’ eyes feature those rod and cone cells too but whereas in humans four out of five cells are rods, in cats it is twenty-five out of twenty-six. The net effect is that whilst cats have much better night-vision than us, they have poorer colour vision. So at night, as long as there’s a glimmer of light, a cat will see you much more clearly than you will see it – but you’ll probably appear almost as ‘grey’ to it as it appears to you.

This link shows how artist Nickolay Lamm has illustrated cat-vision as opposed to human-vision.

But who cares, really, what colour anything is. Let’s celebrate cats-on-beds, purring fit to bust, dribbling copiously and using our toes for mouse-murdering practice. Lets be glad that on a grey winter’s day moggie will come crashing in through the cat-flap to join us by a hearthside blaze, huddle with us over the one remaining bar of the gas-fire or bask with us in wall-to-wall central heating. And there, together, we will sit with our glass of wine/cup of coffee/mug of Horlicks and our copy of Great Expectations/Jonathan Strange and Mr Norrell/ Fifty Shades of Grey/Pregnant with the Rancher’s Baby or whatever, and for a brief spell of time all shall be well, and all shall be well, and all manner of things shall be well with the world.

  • My old cat stretches out his arm,
  • To say, ‘I and You’.
  • He thinks the future threatens harm;
  • I feel it too.
  • The flexing paw to reassure
  • Myself and creature
  • Asserts, in feline comfiture,
  • Our frail, shared nature.
  • Robert Gittings: Cat
  • (my favourite cat poem of all time)

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