“The problem of definitions and of the ‘meaning of terms’ does not directly bear upon historicism. But it has been an inexhaustible source of confusion”.
The second section of Chapter 11 is a critique of the obsession with the definition of terms and the explication of concepts that Popper labeled essentialism. The issue emerges from the ancient problem of universals, whether there are general categories of things over and above the individual instances of things that we observe. Popper was writing about this in section 10 of The Poverty of Historicism and he found that his historical notes on the problem kept growing until he put aside the manuscript of The Poverty and wrote The Open Society instead.
People who habitually address social issues with an imaginative and critical attitude to alternative policies and their likely outcomes will not benefit much from the following critique of verbalism and conceptual analysis. However they may have friends or relations who have picked up bad habits, perhaps at university, and these unfortunates may need professional help.
"The development of thought since Aristotle could, I think, be summed up by saying that every discipline, as long as it used the Aristotelian method of definition, has remained arrested in a state of empty verbiage and barren scholasticism, and that the degree to which the various sciences have been able to make any progress depended on the degree to which they have been able to get rid of this essentialist method. (This is why so much of our ‘social science’ still belongs to the Middle Ages.) The discussion of this method will have to be a little abstract, owing to the fact that the problem has been so thoroughly muddled by Plato and Aristotle, whose influence has given rise to such deep-rooted prejudices that the prospect of dispelling them does not seem very bright. In spite of all that, it is perhaps not without interest to analyse the source of so much confusion and verbiage."
In a nutshell, essentialism claims that true belief (knowledge) results from either (a) an intuitive grasp of the essence of things, or (b) clarification or explication of the concept of the (various) things.
"Like Plato, Aristotle believed that we obtain all knowledge ultimately by an intuitive grasp of the essences of things. ‘We can know a thing only by knowing its essence’, Aristotle writes, and ‘to know a thing is to know its essence’. A ‘basic premise’ is, according to him, nothing but a statement describing the essence of a thing. But such a statement is just what he calls a definition. Thus all ‘basic premises of proofs’ are definitions."
"What does a definition look like? An example of a definition would be: ‘A puppy is a young dog.’ The subject of such a definition-sentence, the term ‘puppy’, is called the term to be defined (or defined term); the words ‘young dog’ are called the defining formula. As a rule, the defining formula is longer and more complicated than the defined term, and sometimes very much so. Aristotle considers the term to be defined as a name of the essence of a thing, and the defining formula as the description of that essence. And he insists that the defining formula must give an exhaustive description of the essence or the essential properties of the thing in question; thus a statement like ‘A puppy has four legs’, although true, is not a satisfactory definition, since it does not exhaust what may be called the essence of puppiness, but holds true of a horse also; and similarly the statement ‘A puppy is brown’, although it may be true of some, is not true of all puppies; and it describes what is not an essential but merely an accidental property of the defined term."
Given that approach the fundamental problem in epistemology and learning is to get hold of the correct definitions or basic premises. Aristotle followed Plato with rather more emphasis on the role of observation in place of Plato's intellectual intuition of the Ideal Forms but in the end he relied heavily on a mental or intellectual faculty that enables us to grasp the essences of things. My introduction to Platonic and Aristotelian essences came in Soil Science I at the University of Tasmania, in an article on soil classication. The author identified three approaches to classification, (1) the Platonic, (2) the Aristotelian and (3) the Instrumental or Practical. For Plato there was a "Heaven" containing ideal types of all the soils, such as the Ideal Podsol ( a kind of soil). All the actual examples of podsols on earth approximate more or less to the ideal. For Aristotle there is no Heaven but instead we build up a picture of the Ideal or Essential Podsol, based on the common features of all the podsols that we observe. The Instrumentalist is not interested in the Heaven of soils, nor the Essential Podsol but classifies soils according to the practical needs of the moment, so he talks about a soil with a heavily leached A horizon (of a certain depth and texture), and a B horison with some other specified characteristics.
The summary of Aristotle's approach is to visualise the growth of knowledge as compiling an encyclopaedia containing the intuitive definitions of all essences, that is, their names together with their defining formulae...
Popper ended the chapter with a brief critique of Aristotle's theory of intellectual intuition, that is, the idea that we have a faculty, intellectual intuition, by which we can visualize essences and find out which definition is the correct one. Popper willingly concedes that we possess something which may be described as ‘intellectual intuition’; and this accounts for the experience of understanding an idea or a process (such as multiplication in arithmetic).
"There are countless intellectual experiences of that kind. But I would insist, on the other hand, that these experiences, important as they may be for our scientific endeavours, can never serve to establish the truth of any idea or theory, however strongly somebody may feel, intuitively, that it must be true, or that it is ‘self-evident’."
He also described how natural scientists have avoided prolonged verbal disputes by refusing to bog down in definitions and the meaning of terms, by ensuring that our statements never depend too much on the meaning of our terms.
"Even where the terms are defined, we never try to derive any information from the definition, or to base any argument upon it. This is why our terms make so little trouble. We do not overburden them. We try to attach to them as little weight as possible...The view that the precision of science and of scientific language depends upon the precision of its terms is certainly very plausible, but it is none the less, I believe, a mere prejudice. The precision of a language depends, rather, just upon the fact that it takes care not to burden its terms with the task of being precise. A term like ‘sand-dune’ or ‘wind’ is certainly very vague. (How many inches high must a little sand-hill be in order to be called ‘sand-dune’? How quickly must the air move in order to be called ‘wind’?) However, for many of the geologist’s purposes, these terms are quite sufficiently precise; and for other purposes, when a higher degree of differentiation is needed, he can always say ‘dunes between 4 and 30 feet high’ or ‘wind of a velocity of between 20 and 40 miles an hour’. And the position in the more exact sciences is analogous. In physical measurements, for instance, we always take care to consider the range within which there may be an error; and precision does not consist in trying to reduce this range to nothing, or in pretending that there is no such range, but rather in its explicit recognition."
Further discussion of essentialism in the context of political economy can be found here, indicating how it has contributed to the collectivist/organic theory of the state. There is a large section on essentialism in Popper's intellectual autobiography Unended Quest. In 'On the sources of knowledge and of ignorance' (Introduction to Conjectures and Refutations) he introduced a table of ideas to suggest that logical confusion of mattters of meaning (on one side of the table) and truth (on the other) has compounded the problem of definitions by confusing the truth of a statement with the source of the statement (as though truth can be assured by going to the right source).