Full Idea
Let all accidents be removed from a lion and a horse. Nothing remains in the intellect to distinguish them. We distinguish a lion and a horse only by analogy to the accidents proper to each. The intellect does not have an essential concept of either one.
Gist of Idea
If you remove the accidents from a horse and a lion, the intellect can't tell them apart
Source
Francis of Marchia (Commentary on Sentences [1330], I.3.1), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 07.3
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.127
A Reaction
What a very nice thought experiment, and very convincing about how the mind perceives such things. But we don't believe horse and lion just consists of the surface properties of them which we experience.