But in addition to things material, it seems that there are immaterial ones which do not pertain as one's own to any particular person. The ideas of which we had occasion to speak before,--immaterial entities, not perceptible by the senses, but thinkable by the intellect, and which severally correspond to all sorts or species of the various material things,--were once conceived as things by philosophers, and they are still so conceived to-day by the majority of men. It is not requisite that one actually think them; it is sufficient that they be in themselves thinkable. As a matter of fact, they may or may not be thought, no differently therefore from any of the material objects which are not created by our senses, but must already exist in order that our senses may perceive them. These ideas are many, in a manner corresponding to the material objects; and they are all different. They mirror, so to speak, the multiplicity of material things in whose semblance and likeness they were devised. There are horses in nature, and there is the idea of the horse by which we are able to recognise all the animals that belong to that species. There are dogs, and there is the dog which we rediscover in every one of them. And there are flowers and the flower; and pinks, roses, and lilies, as well as the pink, the rose, and the lily; and likewise iron, copper, silver, gold, lime, water, and so on, to infinity. It is impossible to set a limit to ideas, because it is not possible ever to stop dividing, distinguishing, subdividing that nature which unfolds itself throughout space.