Thirdly, here is a summary of Russell’s epistemology: his understanding of what knowledge is and how we acquire it. All I have done, in order to understand what BR was saying, is to slightly edit and re-word paragraphs from other sites, to give the nub of what he meant and in plain language. His epistemology was first published in his The Problems of Philosophy (1912).
From here: Russell wrote that there are two ways of knowing objects — by ‘acquaintance’ and by ‘description’. Acquaintance comes from ‘sense data’, which are our immediate perception of colours, sounds, and so on. Everything else, including knowledge of the physical objects themselves, has to be reasoned to by the mind. He called this latter phase ‘knowledge by description’. That is the nub of what has remained influential from his epistemology, although he had later thoughts.
(The following paragraphs, slightly paraphrased and edited, are from sparknotes on Russell unless otherwise stated. The latter website on Russell seems presently to have changed its subdivisions. In my effort to make the interpretations from sparknotes logically consistent in my own mind, I may have got some of them a little wrong, but they satisfied me that they gave me an understanding of Russell’s depths of logicking.)
BR was an Empiricist who thought that all knowledge comes from sensory perceptions, i.e. our sense-data.. These however can be erroneous: If three people—one tipsy, one feverish, and one colour-blind—look at the same table, they will see it differently. If the table itself is under water or behind wavy glass, it will again be seen differently.
So how can we rely on sense-data to tell us about the real object?
But BR now deserted the strict logicking of Philosophy, and accepted the commonsense view: That a hundred different viewers may have a thousand different kinds of perception, yet each agrees they are looking at the same table!
‘Sense-data’ was a term coined by Russell; they are the mental images (visual, auditory, olfactory, tactile, and gustatory) we receive from the physical object. Sense-data are related to the physical objects they represent, though the nature of this relationship is unclear. The skeptical argument through the ages was that sense-data tell us nothing about the reality of the object!
To the instinctive belief that the same table exists despite variable sense-data, Russell adds the hypothesis that the physical objects themselves actually cause the sense-data and therefore correspond to them in some way.
The sense-data produced by physical objects are then received and processed by our minds. Russell calls the result ‘perceptual knowledge’. (‘Perception’, ‘appearance’, ‘experience’, all seem to mean the same.)
Not only do we have perceptual knowledge from sense-data mentally-processed, but BR believed we also have various kinds of a priori knowledge independent of what comes to us from the outside world. These include the self-evident rules of logic and of mathematics.
Perceptual knowledge (the knowledge of things) and a priori knowledge (which he seems to have called ‘the knowledge of truths’) work together: the first gives us empirical data, and the second tells us how to process that data. (Does that mean that logic helps us process sense-data so as to give us knowledge that there is actually a table out there?)
To enlarge on BR’s knowledge by acquaintance and knowledge by description: To be acquainted with something is to be aware of it by sense-data. When you see and sit on a red plastic chair, you become acquainted with its redness, smoothness, coolness and hardness.
But to know that this thing is called a “chair” and often found with other “chairs” and something called a “table”, requires us to make inferences, based on our general knowledge of facts and on our acquaintance with other similar objects.
Russell called this kind of knowledge ‘derivative’ or ‘by description’. For instance, we know only by description, and not by acquaintance with sense-data, that Everest is the tallest mountain in the world. Few of us have been there, and even then we would have to have measured Everest and all the other mountains in the world. So we have to rely on the testimony of others to “know” that Everest is the tallest mountain.
Just as we know objects immediately (by acquaintance) or derivatively (by description), so we also know truths ( ‘a priori knowledge’) immediately or derivatively. Russell defines immediate knowledge of truths as intuitive ones. These are concepts so clearly self-evident that we just know they must be true, such as ‘1 + 1 = 2’. Derivative knowledge of truths however involves deduction and inference from self-evident truths. (We need examples of these latter derivative kinds of a priori knowledge but I didn’t get them.)
To continue with sparknotes here on Russell’s epistemology (in his The Problems of Philosophy):
Some philosophers didn’t agree with BR’s assumption that sense-data are the beginnings of our recognition of objects. They said that we are immediately aware of the table itself, and only with conscious concentration do we become aware of sense-data (from here).
Some critics also said that The Problems of Philosophy was an introduction, and Russell’s arguments aren’t thorough. He often ‘illustrates’ his points rather than ‘meticulously mapping them out’.
Also that, while there are appeals to common sense, there are unconvincing elements. One such is that Russell never satisfactorily explains what exactly makes a truth (presumably an a priori one) ‘intuitive’, ‘immediate’, ‘self-evident’, and that he doesn’t provide sufficient examples of them. And that he also provides no way of distinguishing between two apparently self-evident truths that contradict each other. (No examples are given for this last sentence.) (from here.)
He continued his epistemology in his book Our Knowledge of the External World and in an article The Relation of Sense-Data to Physics (1914) .
To repeat: In line with British empiricism, he thought that sense-data ( knowledge by acquaintance) is the beginning of all knowledge.
From here: BR brought up the example of what we think we know about Julius Caesar. All of it in fact comes solely by description and not by acquaintance (unless, think I , we can say that all this knowledge by description comes via our acquaintance with the descriptions.) This seems to foreshadow what he says under his later logical atomism, that statements can be broken down into constituent assumptions. When we use the term ‘Julius Caesar’, we’re using the name to refer not to the man himself but to descriptions of purported facts we have learned about him.
The argument is also tied to Russell’s Theory of Descriptions, see here, which explains how definite descriptions—that is phrases like ‘that cat’, ‘Bill Cosby’, or ‘my mother’, which refer to specific objects—are just shorthand for a series of logical claims.
From here: Russell’s attempt to discern what kinds of knowledge could be considered reasonably certain is similar to the goal of Principia Mathematica, which is to find an undeniable reason for believing in the supposed truths of mathematics. Both the mathematical and the epistemological branches o f BR’s work have at their heart his devotion to rigorous analysis and his reluctance to accept any proposition (no matter how obvious or commonsense seeming) without a concrete, logical reason for doing so.
The following is a collection of BR’s thoughts as they appear on the Web, that I haven’t sufficiently understood, but they seem to relate to his epistemology, to his worrying about what Knowledge is and how we acquire it:
To start with (from here, and often verbatim): BR wanted to be sure of the relationship between knowledge, perception, and physics. He accepted Descartes’ opinion that the foundation of knowledge is each person’s individual consciousness. But how can a theory of knowledge for all people be built on someone’s private experiences? It was a difficult logical leap from the “private space” of personal sensation, to the “public space” of science and the physical world.
Now I seem to return to what BR has already developed above (from here):
He had previously argued that ‘sense-data’ were caused by the objects and then perceived by our senses: A cat exists in the real world, and from it we sense warmth, softness, grayness. The problem is that we are then only acquainted with the sense-data—we have to infer that a cat is causing them, but we cannot know for sure that such a thing exists. (I would have thought surely that this theory that things really just exist through their sense-data had been raised previously in the long history of Philosophy.)
Russell then argued that the most fundamental principle of scientific reasoning is: “Whenever possible, logical constructions are to be substituted for inferred entities.” (This seems to mean that we should stick to the logical reasoning that there is a cat and not assume that the cat does actually exist.)
But BR now seems to do an about-turn: Instead of continuing to say that physical objects create sense-data, he now argues that sense-data construct the physical object! Sense-data don’t just logically infer the existence of physical objects, but they essentially create them! (Is BR now saying that the sense data are all there actually is, and that there is nothing outside of them? This seems to conflict with what was said above, that BR was a realist who believed that the sensed world actually existed separately from our sensations of it.)
This new theory of BR’s goes along with what he now called ‘sensibilia’. These are ‘unsensed sense-data’— how an object appears when no one is perceiving it. This accounts for an object’s continued existence in the absence of perceivers. (Again, that to me sounds like Idealism, even like Berkeley’s neat idea that God is keeping an object in existence by always perceiving it. BR had previously called Idealism ‘poppycock’.)
Russell was an Empiricist, who believed that everything we know must be acquired through the senses. He also believed against the Idealists that the outside world existed whether we see it or think about it or not. He thought Idealism was poppycock. (Presumably he was able to argue it out logically like a philosopher should, rather than just saying ‘poppycock’.)
So, sense-data are not simply images in the mind but are the building blocks of physics (from here). Thus, sense-data inhabit the public space of science as well as the private space of experience. (No, I am too dense to see how this theory of sense-data and sensibilia closes the gap which BR thought to exist between the private and public spheres.)
The next three paragraphs are derived from here, often verbatim: ‘In linguistics, Russell showed how ordinary statements could be analyzed to a string of simpler, more elemental assumptions, which could then individually be judged either true or false.’ (This refers to BR’s Logical Atomism, here,)
‘Russell shows how a logical atomism can also apply to… knowledge of the physical world. He combines logical atomism here with empiricism.’ The atoms of our knowledge are the sense-data of direct acquaintance. These comprise the only knowledge we can genuinely claim. ‘All other knowledge is inferred or deduced from it.’
‘Consider the cat. Its sense-data—warmth, softness, grayness—are the “atoms” of our knowledge about it. The cat that we infer from the sense-data is only a “logical fiction.” Objects are nothing more than systems of sense-data.’ Hence there is ‘Russell’s assertion that sense-data create rather than simply testify to the existence of physical objects.’!
And the next four paragraphs (?and more) are from here, often verbatim:
‘After advancing his theory that sense-data create the physical world, Russell abandoned it…and reverted to the notion that physical objects could legitimately be inferred from sensory experience.’ (So does BR now abandon the idea that all we know are sense-data, and accepts that an object actually exists independently of its sense-data? That is a little confusing in that the quoted sentence seems to say that objects can be ‘inferred’ but also that they actually exist).
‘This [shift of Br’s] was partly due to advances in physics and physiology, which showed that perception is caused by the physical world on our sense organs.’
Also, as I seem to understand, BR came to wonder, as we all must, about what he had called ‘unsensed data’. How on Earth can there be sensation when no one is present to do the sensing? And it also seems he couldn’t now understand what he had meant by ‘private’ and ‘public’ spaces or how sense-data and sensibilia interacted with them.
‘In later work like The Analysis of the Mind (1921), Russell stops treating sense-data and the act of sensation as separate entities. He does, however, maintain the classic empiricist position that physical objects are not directly knowable; only their sensory effects… are… ‘ (Oi! say I, that’s Philosophy!)
‘Eventually, Russell abandoned his inquiries into the relationship between matter and perception, though he continued to work in other areas of epistemology.’
It says that other philosophers, including Wittgenstein, found flaws in BR’s idea that the elemental units of knowledge of the physical world are sense-data, i.e. his logical atomism applied to epistemology. (But BR’s idea seems to me so unexceptional that I don’t see how W. could have objected.)
‘Although Russell’s….logical atomism may have proved untenable, it remains an important moment in the history of philosophy.’ !!