Not an easy read, but fun at times. How do we know what is real? There is a disjunct between appearance and reality. In other words, the “real” is not always the obvious. Russell’s main sparring partner is Bishop Berkeley, and so Russell treats us to a fine display of Idealism (with following refutations). Berkeley says that if things exist independently of us, they cannot be the immediate objects of sensation. Idealists, therefore, place the existence of objects within the mind (or rather, say such existence is mental). What is known in the senses is not the immediate object of the senses.
For Berkeley an idea is what is immediately known (sense-data). This means x is “in” the mind. This raises a problem. What does it mean to be “in” the mind? It’s better to say an object is “before” the mind. Berkeley equivocates on “in.” All he has a right to say is the thought of x is within the mind. Berkeley did not distinguish between the thought of something and the act of thinking that thought. The latter is certainly mental, but we are not justified in saying the former is.
Different Types of Knowledge
Knowledge by acquaintance is “foundational” knowledge. It is immediate and direct (Russell 48).
Universals
Russell correctly calls “universals” “ideas.” This way there is no confusion on what Plato meant by ideas and what Berkeley and Locke mean by ideas. We are aware of universals by “conceiving.” As conceived, the universals are now “concepts.”
A universal is the opposite of that which causes sensation. A universal is that which is shared by many particulars. Proper names stand for particulars, while other substantives stand for universals.
Other examples of universals are “qualities” and “relations.” Many relations do not exist in space or time, yet they are real and can be known to be real. Take the phrase, “North of London.” “North of” is not physical, yet it is a real something. The implications of this for Christianity, which presumably Russell didn’t explore, are staggering.
The Problem of Induction
When two things have been found to be associated together, and no instance is known of one occurring without the other, does the occurrence of one give me any ground for expecting the other?
No.
Experience only tells us about past futures. It cannot tell us what to expect of future futures.
Conclusion
I think Russell does a successful job in showing that we can have legitimate knowledge that isn’t derived from sensations. Further, this work has a number of semi-legendary chapters along with a fine bibliography.
Appearance and Reality
What is the “real” object? If I am looking at the table, is the table’s appearing to me the real table? If I look at it under a microscope, I will see something different. Which, then, is the real table? Russell suggests the “real” is not what we see. It is inferred from what we see (Russell 11).
Russell suggests, rightly I think, that if we keep “reducing” matter all the way down we will end up with electrical forces (16). This is correct. But why stop there? Why not reduce the electrical forces even further? He gives no answer, but it’s not hard to fathom: any further reduction, to quote Matthew Raphael Johnson, will show that energy will have a non physical cause: Logos. In other words, Logos is the substrate of the energy. Objects within space and time can be reduced to forces, and these forces must be outside space and time. Russell later admits that real “somethings” can exist outside space and time (98).
The Existence of Matter
If an object is merely sense-data, then it will cease to exist once it is no longer perceived. But this is silly. If I throw a blanket over a table, does the table cease to exist? If so, then is the blanket floating in mid-air (!?).
I am the King's Man 
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