“24. It is very obvious, upon the least inquiry into our thoughts, to know whether it be possible for us to understand what is meant by the _absolute existence of sensible objects in themselves, or without the mind_. To me it is evident those words mark out either a direct contradiction, or else nothing at all....” Again there is a very remarkable passage in Section 10, of the fourth Dialogue of Berkeley’s _Alciphron_. I have already quoted it, at greater length, in my _Principles of Natural Knowledge_: “_Euphranor._ Tell me, Alciphron, can you discern the doors, window and battlements of that same castle? _Alciphron._ I cannot. At this distance it seems only a small round tower. _Euph._ But I, who have been at it, know that it is no small round tower, but a large square building with battlements and turrets, which it seems you do not see. _Alc_. What will you infer from thence? _Euph._ I would infer that the very object which you strictly and properly perceive by sight is not that thing which is several miles distant. _Alc._ Why so? _Euph._ Because a little round object is one thing, and a great square object is another. Is it not so?...” Some analogous examples concerning a planet and a cloud are then cited in the dialogue, and this passage finally concludes with: “_Euphranor._ Is it not plain, therefore, that neither the castle, the planet, nor the cloud, _which you see here_, are those real ones which you suppose exist at a distance?” It is made explicit in the first passage, already quoted, that Berkeley himself adopts an extreme idealistic interpretation. For him mind is the only absolute reality, and the unity of nature is the unity of ideas in the mind of God. Personally, I think that Berkeley’s solution of the metaphysical problem raises difficulties not less than those which he points out as arising from a realistic interpretation of the scientific scheme. There is, however, another possible line of thought, which enables us to adopt anyhow an attitude of provisional realism, and to widen the scientific scheme in a way which is useful for science itself. I recur to the passage from Francis Bacon’s _Natural History_, already quoted in the previous lecture: “It is certain that all bodies whatsoever, though they have no sense, yet they have perception: ... and whether the body be alterant or altered, evermore a perception precedeth operation; for else all bodies would be alike one to another....”