I’ve been reading Brand Blanshard’s book The Nature of Thought (1939) recently. A treatise of over a thousand pages, the length itself is already out of fashion; few people nowadays write for an audience with that long of an attention span. The subject matter too is out of fashion. It’s about the introspective psychology of “thought,” with Blanshard defining that term in the context of the book as what’s either true or false. For example, sensation is neither true nor false—at least that’s true insofar as we define that term in the same way as Blanshard, which is one of the standards definitions and probably the most useful one. But perception is different. The sensation of a speck moving in the sky just is what it is, but the perception of the speck as an airplane is either true or false.
In modern logic, it’s standard to define the term “proposition” as what’s either true or false. The modern logician focuses on the words: “A speck moving in the sky” is neither true nor false, which means that it’s not a proposition, but “the speck moving in the sky is an airplane” is different; it’s a proposition. Introspective psychology being out of fashion, the modern logician’s analysis stops there. It doesn’t point out that the former is sensation and the latter is perception.
What’s the subjective experience of believing that something is true? That’s a question that David Hume (1711-1776) asked. What his answer was and whether it was right is beside the point; he at least asked the question and tried to answer it. For Hume (and the rest of the British empiricists, which included the 19th-century phenomenalist holdout in logic John Stuart Mill), there was no distinction between the kind of introspectionist work in Blanshard’s The Nature of Thought, which was the introspective psychology of propositional thought, and what’s salvageable in anti-introspectionist modern logic, which is about propositional thought reflected in words and other symbols (with what the mind is doing in interpreting the words and other symbols being left unanalyzed, how dangerous that is notwithstanding).
Ultimately, we must integrate British empiricism with modern logic. We must analyze sensation and perception, the subjective experience of believing that something is true, etc., which is the foundation (epistemologically speaking), before analyzing propositional thought reflected in words and other symbols, which builds on that foundation.