Cause Means Regular Association
Classic Philosophical Questions Part 5 - Knowledge
David Hume, from An Enquiry Concerning Human Understanding
Kem Stone - 25 November 2007
The concept of necessary connection, or cause and effect, is one most people including myself take for granted.  
Until I first read Hume, it had never even occurred to me to question exactly what it means to think that one event
causes another, or that all of our scientific knowledge rests on the presupposition that certain events are
connected by necessity.  This text is Hume’s argument that the ideas of cause and effect do not come to us by
direct observation, but through regular association of events, and that the connection is not in the objects
themselves but only in the minds of the observers.

Hume begins with the nearly universally accepted proposition that all of our ideas are copies of our impressions:
that we cannot think anything that we have not felt in one form or another with our senses.  When we apply this
logic to the ideas of cause and effect, we are confronted with the fact that we never directly observe any
connection between a cause and its effect, but only that one event follows another.  “From the first appearance of
an object, we never can conjecture what effect will result from it.  But were the power or energy of any cause
discoverable by the mind, we could foresee the effect even without experience, and might, at first, pronounce with
certainty concerning it, by mere dint of thought and reasoning” (305).  The properties of objects we do observe—
solidity, extension, motion—are complete in themselves and say nothing about the kinds of events that may follow
from them.  Hume therefore concludes that the idea of power can not be derived from the observation of objects.

One special case that it may be put forward provides us with the idea of power in the command of the human will:
it seems that our minds have the power to move parts of our body through direct volition.  But upon reflection we
find that the mechanism of this connection also escapes our observation.  “The motion of our body follows upon
the command of our will.  Of this we are every moment conscious.  But the means by which this is effected, the
energy by which the will performs so extraordinary an operation, of this we are so far from being immediately
conscious that it must for ever escape our most diligent enquiry” (306).  Hume gives three reasons.  First is the
fact that the union of soul and body—or how the immaterial is able to affect the material—has always been one of
philosophy’s greatest mysteries, and would be no more mysterious if our will were able to move mountains or
control the planets in their orbits.  Second, not only can we not move mountains, but we cannot control some
parts of our own body such as the heart and liver as we can the arms and legs.  And finally, the study of anatomy
shows that our will does not move the body by direct volition, but through a chain of events running from the brain
through the nerves and muscles and only bringing about the full movement at the end of the process.  The mind
wills a certain event but the actual effects are very different, and since the effects are unknown the original power
itself is unknown.

Hume asserts that the attribution of events to causes is a habit of the mind that results from the observation of
certain events that regularly follow one another.  Events that occur with great regularity, such as the descent of
heavenly bodies, the growth of plants, and the nourishment of bodies by food, never even raise questions about
causality.  It is only extraordinary phenomena such as earthquakes and pestilences that put us at a loss to assign
proper causes and to explain how the effects follow from them.  But “even in the most familiar events, the energy
of the cause is as unintelligible as in the most unusual, and that we only learn by experience the frequent
Conjunction of objects, without being ever able to comprehend anything like Connexion between them” (307).

Because we never have any direct experience of these phenomena, Hume’s conclusion seems to be that the
words
power, connexion, cause and effect are meaningless in any context.  But although we can never
conjecture from one experience of a certain event what event will follow, “when one particular species of event
has always, in all instances, been conjoined with another, we make no longer any scruple of foretelling one upon
the appearance of the other” (308) and call one
cause and the other effect.  These words do have meaning, but
not in the sense that is usually presupposed.  The connexion is something which we
feel in the mind, but nothing
more.  The first time a man sees the communication of motion of one billiard ball striking another, he can not say
that these events are connected, but after witnessing the same event over and over again, a connection is formed
in his mind.  “When we say, therefore, that one object is connected with another, we mean only that they have
acquired a connexion in our thought, and give rise to this inference, by which they become proofs of each others’
existence” (308).

Hume does not wish to underemphasise the importance of cause and effect, which he admits are the foundations
upon which all of our scientific reasoning is based.  The utility of science is to predict future events by identifying
effects with their causes.  Hume’s conclusions merely show us that any definition we can come up with concerning
cause and effect will be incomplete at best.  Hume offers two definitions, the first based on the fact that similar
objects are always conjoined with similar.  “Therefore, we may define a cause to be
an object, followed by
another, and where all the objects similar to the first are followed by objects similar to the second
.  Or in
other words,
where, if the first object had not been, the second never had existed” (309).  The second
definition has to do with the mind’s transition to the idea of effect upon the appearance of a cause.  “We may,
therefore…call it
an object followed by another, and whose appearance always conveys the thought to that
other
” (309).  According to these definitions, the idea that the vibration of a string causes a sound can either mean
that all similar vibrations are followed by similar sounds, or that upon the appearance of the sound, the mind forms
the idea of the vibration.

I am sure it would be impossible to completely refute the claims that Hume makes here, but I do not see this as a
reason to abandon our convictions concerning cause and effect.  It is of course the case that we do not directly
perceive any causal connection between an event and that which follows, and that this connection is formed
merely in our minds only after repeatedly witnessing the same conjunction.  However, I do not take this to indicate
that the concepts of cause and effect are exclusively creatures of human invention.  The universe operates
according to these very phenomena.  One event
causes another.  A meteor strikes the ground and a crater is
formed.  These events
are connected, whether perceived by a human mind or not.  If a bullet enters a man’s brain
and he dies an instant later, I may not be able to perceive any causal connection between these two events, but it
does not require a lengthy philosophical argument to conclude that the bullet was the
cause of his death and not
just a random event that happened to occur by astonishing coincidence at the moment he dropped dead.

Cause and effect are every bit as real as the world of corporeal objects, and as such they suffer from the same
lack of immunity to doubt as everything else.  We do not directly perceive the external world any more than we
directly perceive causation.  What we perceive is merely our brain’s interpretation of electrical signals, and it could
be quite mistaken about everything.  Yet as long as there is no good reason to doubt the existence of the external
world, there is no reason to doubt the concrete reality of phenomena as fundamental to the way this universe
operates as cause and effect.  What these phenomena represent is nothing more or less than the interconnectivity
of everything that has ever existed.  No event is without a cause, nor is any cause without an effect.  History is a
long chain of causes and effects stretching all the way back to the only event in which causality can be doubted:
the very beginning.  As to whether the universe itself has a cause, and whether there exists anything uncaused, is a
matter for an entirely separate branch of philosophy.  But as far as epistemology goes, I believe it is perfectly
acceptable to presuppose the existence of cause and effect, whether purely on pragmatic grounds or merely for
the sake of coherence.  Without cause and effect, all of our knowledge crumbles and we are left with nothing but
doubt, so we may as well consider them to be as real as anything else.