 Locke distinguishes two sorts of probable propositions. The first of these have to do with particular existences or matters of fact, and the second that are beyond the testimony of the senses. Matters of fact are open to observation and experience, and so all of the tests noted above for determining rational assent to propositions about them are available to us. Things are quite otherwise with matters that are beyond the testimony of the senses. These include the knowledge of finite immaterial spirits such as angels or things such as atoms that are too small to be sensed, or the plants, animals or inhabitants of other planets that are beyond our range of sensation because of their distance from us. Concerning this latter category, Locke says we must depend on analogy as the only help for our reasoning. He writes: