Hume’s Causality Problem: An Introduction

I was reading through Trin’s very interesting post on the epistemic minimalism of causality in relation to Judea Pearl’s response to Bertrand Russell’s problem, as well as Josh’s subsequent thought provoking comment on Hume, which got me thinking this week about how philosophy has historically reached this point and why this is conceptually so important.

Arguably, the foundational thought of modern philosophy (for us philosophers that means 1600’s through some point in the 1900’s), is that the only knowledge that can be known with certainty is purely analytic (ideas in logic or math we can analyze) and thus a priori (knowable both prior to and independent of empirical based experience); and that all empirical knowledge of the world (biology, physics, engineering, medical science, what your spouse is thinking, what sports team will win) is probable only and can never really be known.  You could doubt your eyesight, you could have a false memory as a witness to a crime, you could have a car accident and hallucinate imaginary events, or could believe someone is loyal to you but is lying, etc.  This might not look it but this is a BIG ubiquitous problem.  The upshot of the empiricist philosopher David Hume is that if you accept both of these premises it is essentially impossible to escape skepticism, by which we mean philosophical skepticism.  This commits us to the ultimate epistemological (general theory of knowledge) problem, whereby nothing in the world can constitute knowledge of nature or sociality or our own identity.  You might think, ok well sure once in a while something could be a false memory or a hallucination but surely that is generally rather rare?  This understandably is where the charge comes into play that there are two kinds of philosophers: the ones on the street walking to class acting and making causal based decisions like a normal person, and the ones in class doubting causal existence and the justification for any necessary connection.  Nonetheless it is a genuine problem in the theoretical foundations of any discipline.

The problem is causation: If event x, then event y.  As an empiricist, Hume was committed to all knowledge arising out of our sense perceptions to form simple and complex ideas that govern our understanding.  Thus, Hume was determined to trace the object or event we see in the world that physically represents causality itself.  Hume’s problem in A Treatise of Human Nature was that he could not find one.  Nonetheless, Hume posited three aspects of any causal relation in the world: contiguity, priority, and necessary connection.  All causality shares the relational property of being contiguous in time and space, as well as priority (cause precedes effect), and that there exists a necessary connection between one event causing the second event to happen in the world.  As Hume shows in An Enquiry Concerning Understanding, there is no justification for asserting necessary connection in causality, which in term undermines the foundation of the uniformity of nature and the regularity order of knowledge.

In philosophy this is known as the problem of induction, which neatly follows the lines of Hume’s Fork (possible total of knowledge equals matters of fact and relations of ideas).  Matters of fact are any empirical based data or knowledge of the world (the bird is in the tree, the car is blue), whereas a relation of ideas is a truth of reason alone (2 + 2 = 4, or If x is y, and y is z, then x is z).  Inductive inferences (theory of prediction of future events based on data) are about the world and contain probability and deductive inferences (necessary reasoning) are about logical and mathematical inference and are a priori.  This has been a general feature, and an unwieldy problem, for four hundred plus years.  Contemporary philosophers have tried to answer the modern problem of skepticism in many ways, such as Popper attempting to make science deductive or some continental and post-analytic philosophers just accepting the problem as unsolvable and moving on (though they would say the problem disappears as a question by unifying subject with object in the dissolution of the interpretation of the self and other but that never struck me as satisfactory but sounded more like an Eastern mystical retreat to me).

In a post-Hume world, intellectuals are still trying to resolve the problem of skepticism (though it seems in the later 20^th century people just got tired of it and moved on without bothering anymore) and it remains an open problem.

Next I would like to explicate Hume in more detail and tie this in with Trin’s post vis-à-vis C.I. Lewis (Clarence Irving Lewis the logician, epistemologist and moral philosopher, not that fat bald cigar chomping Christian that wrote Chronicles of Narnia).