For the last couple of weeks I’ve been reading Karl Popper’s The Logic of Scientific Discovery, a true masterpiece of the philosophy of science. Both intellectually rich and clearly and persuasively written, the book really is a joy to read. This post is my attempt to get to grips with one of the knottier problems considered within it, that of the empirical basis.
Falsifiability and Basic Statements
When I’m asked why anyone should bother to study philosophy, one of the advances I mention is Popper’s introduction of the condition of falsifiability (as opposed to the verificationist stance of the logical positivists) as that which distinguishes the statements of science from those of non-science. In his own words (with his emphasis):
We must choose a criterion which allows us to admit to the domain of empirical science even statements which cannot be verified. But I shall certainly admit a system as empirical or scientific only if it is capable of being tested by experience. These considerations suggest that not the verifiability but the falsifiability of a system is to be taken… it must be possible for an empirical or scientific system to be refuted by experience.
This is eminently sensible. How, for example, could one hope to verify that Newton’s law of universal gravitation holds between all masses in the universe, for all time? But if Newton’s law were false, the act of falsification would simply involve observing an instance in which certain masses failed to attract each other as predicted. Thanks to Popper, this condition is now generally known and accepted by the scientific community (physicists will dismiss an unfalsifiable theory as ‘not even wrong‘).
The crux of Popper’s principle is this: a statement of a scientific theory should be universal. Roughly speaking, it asserts something about all entities with some given property. On the other hand, the statements which humans can make based on their own experience are basic; they correspond to particular events. The difference is that between the statements ‘All swans are white’ and ‘This swan is white’. The latter can, in principle, be conclusively decided one way or the other; the former cannot be conclusively verified, only falsified.
From a universal statement, we can deduce a multitude of basic statements. The negation of any one of these basic statements will falsify that universal statement. For example, the existence of any one black swan will disprove the theory that all swans are white.
To the contrary (and this is Hume’s problem of induction), we cannot infer a universal statement from the conjunction of any finite number of basic statements. In our example, no matter how many white swans we observe, we cannot conclude that all swans must be white.
To digress for a moment, we might ask, what about the statement ‘All swans currently living on earth are white’? It is an ‘all-statement’, but can, in principle be conclusively decided. As this refers to entities within a bounded region of spacetime, Popper distinguishes this as a numerically universal statement, as opposed to a strict universal statement; only the strict universal statements are those which Popper sees as being characteristically scientific.
The Empirical Basis
Now we get to the problem mentioned in the title of this post, the problem of the empirical basis. The problem: what precisely is the relationship between perceptual experiences and basic statements?
Clearly a basic statement, one which describes an event, has its source in the experience of someone’s senses. On the other hand, the rules of logic only give us the means to deduce statements from other statements, not from experiences. To Popper, the great danger is that of falling into the trap of what he terms psychologism; the view that basic statements are at bottom justified by a statement of the type ‘I am personally convinced that so-and-so is true’. It’s plain to see why allowing justifications of this nature will play havoc with the rational search for truth.
What is Popper’s solution to this problem? He abandons any notion of logically justifying basic statements. Instead, “basic statements are accepted as the result of a decision or agreement; and to that extent they are conventions”. Much like in statistical hypothesis testing, we do not exactly assert the truth of a basic statement; we simply decide whether to accept or reject it. This is a procedure based on rules, but we do not have any absolute guarantee that this procedure will give us the correct result – any more than we can guarantee that a jury’s verdict in a criminal trial will be the correct one.
To Popper, the role of sense experience is to provide evidence which can be used to arrive at a decision – but ultimately, the acceptance or rejection of a basic statement is a decision.