“Is there any knowledge of the world which is so certain that no reasonable man could doubt it?”
This is the first sentence of Bertrand Russell’s The Problems of Philosophy (1912). Not having previously read anything by Russell but having a sort of passing acquaintance with his legacy, I expected (and feared) that he would devote most of his attention to logic. I expected him to transform ordinary sentences like “The cat is on the mat” to strangely annotated equations from which various inductions and deductions could be drawn. Happily, Russell touched barely at all on such arcana.
Mostly I’d say that Russell’s book is a concise elaboration on realism. In the first chapter, “Appearance and Reality,” Russell notes that the sensory impressions we get from, say, a wooden table, vary depending on the angle at which we view the table, the lighting, the scale of inspection (raw vision versus microscope), and so on.
“Thus it becomes evident that the real table, if there is one, is not the same as what we immediately experience by sight or touch or hearing. The real table, if there is one, is not immediately known to us at all, but must be an inference from what is immediately known. Hence, two very different questions arise; namely (1) Is there a real table at all? (2) If so, what sort of object can it be? (p. 11)
Russell answers the first question in the affirmative: there is a real table existing independently of the individual human observer and of intersubjective consensus. It is the real table that causes our sensory impressions of it.
“The real table, if it exists, we will call a ‘physical object.’ Thus we have to consider the relation of sense-data to physical objects. The collection of all physical objects is called matter.” (p. 12)
Russell dismisses as implausible and unduly complicated the idea that we create the sense-data about the world rather than apprehending it. E.g., suppose Russell sees a cat on one side of the room, then a minute later he sees it on the other side of the room. Russell deems it more likely and less intellectually baggy that a real cat moved unnoticed from one side of the room to the other, rather than than that Russell created two separate sensory impressions of a cat, first in one place, then in another, in a room which is itself merely a sensory projection of Russell’s mind. Intersubjective agreement as the source of what we purport to know about the world he likewise rejects. After all, we are acquainted with other people in the same way we know about tables: through sense-data. In short, the common-sense notion of a really existing external world populated with material things seems the most acceptable explanation of our experiences and thoughts about the world.
If real material objects cause our sensory impressions of them, then what are these objects actually like? Russell is prepared to accede to the findings of natural science. As to what science actually has to say on the matter Russell is fairly vague. He talks about stationary objects and motion and space, but he never discusses forces that act on objects or that impel motion. Of course this is a philosophy book and not a science book.
Eventually Russell does talk about logic, but he spends practically no time at all evaluating the logic of mathematical or linguistic statements in and of themselves. Mostly he insists that language, like sense data, is about something other than itself. If I say “The school is between the house and the mountains,” what’s most important about this sentence is the information it conveys about the relative positions of real things in the real world.
A statement is true to the extent that it conveys accurate information about those aspects of the world it describes. In other words, Russell contends that truth corresponds with facts about the real world. He’s not prepared to define “fact” precisely; e.g., “The grass is green” is true in that it corresponds with sense-data facts about the grass even if it doesn’t correspond with scientific facts about the “real” grass which causes the sense-data. Suppose I encounter a new statement that conveys content consistent with a body of other statements generally regarded as true. This sort of inter-statement coherence may increase the likelihood that the new statement will likewise prove to be true. However, coherence among statements doesn’t make them true, either individually or collectively: the whole pack of statements might all be false in similar ways.
The purpose of this book, first published a hundred years ago, is to introduce the big questions of philosophy, so Russell doesn’t go into great detail in justifying his answers. What strikes me, as someone who hasn’t studied philosophy, is Russell’s quite thoroughgoing (though not unalloyed) realism. My understanding is that Russell was an influential figure in the split of Anglophone analytic philosophy from continental philosophy. I presume that the analytics’ commitment to realism has generally persisted, but that the focus of their philosophical work shifted to mathematics and logic and language mostly because the philosophers regarded science as the proper field for investigating the nature of reality.