Transcript Humes Old and New: Cartesian Fellow

David Hume:
Scepticism, Science,
and Superstition
4. Hume’s Argument
concerning Induction
Dr Peter Millican
Hertford College, Oxford
A Very Brief Overview
Suppose we see A followed by B again
and again. When we next see an A, we
naturally infer a B. But why?
– A Priori insight? No: a priori, we can know
nothing whatever about what causal effects A
will have. “Intelligibility” is just an illusion.
Such factual inference is clearly based on
extrapolating into the future the
associations that we have observed.
2
Inferring Uniformity
What ground can we give for extrapolating
from observed to unobserved?
– Logical intuition? No.
– Deductive reasoning? No: neither of these,
because it’s clear that extrapolation could fail,
so it can’t be a matter of pure logic.
– Sensory knowledge? No: what we perceive
of objects gives us no insight into the basis of
their powers, hence no reason to extrapolate.
– Experience? No: that would be circular.
3
Hume’s Argument in Context
The Argument in the Treatise
– The Argument concerning Induction (“the
Argument”) appears in Treatise I iii 6, the
Abstract, and Enquiry IV.
– In the Treatise, the Argument is embedded in
an extended discussion of the origin of the
idea of causal necessity. This distorts it:
4
A bit muddled about causal cf. “probable” inference;
Doesn’t clearly distinguish between psychological
mechanism cf. epistemological foundation;
Also omits some important stages.
Hume’s Mature Argument
The Argument in Enquiry IV
– Totally separated from discussion of the idea
of causal necessity (in Enquiry VII);
– Explicitly centred around epistemology: “what
is the nature of that evidence, which assures
us of any real existence and matter of fact,
beyond the present testimony of our senses,
or the records of our memory”? (E 4.3)
– More complete than Treatise, e.g. explicit that
senses and intuition cannot ground induction.
5
Inference from Impression to Idea
Treatise I iii 6 focuses on what Hume takes
to be the paradigm causal inference:
– After seeing A followed by B numerous times,
we see an A (i.e. we have an impression of A)
and expect B (i.e. we form a lively idea of B).
– This tendency to infer from A to B underlies our
ascribing A as the cause of B: “the necessary
connexion [i.e. our belief in causal necessity
connecting A to B] depends on the inference”,
not the other way round (T 1.3.6.3).
6
Hume’s Fork
Enquiry IV starts from the distinction between
“relations of ideas” and “matters of fact”.
– Relations of ideas can be known a priori by
inspecting ideas; hence their falsehood is
inconceivable and they are necessarily true.
– Matters of fact can be discovered only through
experience, since their falsehood is conceivable
and they are contingent (could be true or false).
This is a refinement of the distinction
between types of relation in T 1.3.1.1-2.
7
Demonstrative and Probable
A Lockean distinction:
– In demonstrative reasoning, each link in the
inferential chain is “intuitively” certain (hence =
“deductive” in the modern non-formal sense).
– In probable reasoning, some links are merely
probable (hence = “inductive” in a loose sense).
For Locke, both involve rational perception:
– Reason perceives the links in a demonstrative
argument, by “intuition”.
– Reason also perceives probable connexions.
8
Hume on Types of Reasoning
In Treatise I iii 6, Hume employs Locke’s
terminology. But in the Enquiry …
– Demonstrative inference is also called
“reasoning concerning relations of ideas”.
– Probable inference is usually called “moral
reasoning” or “reasoning concerning matter of
fact” (I call this factual inference for short).
– Factual inference is ampliative reasoning,
which draws conclusions beyond what can be
inferred a priori by relations of ideas.
9
Hume’s Factual Inference
Consider:
Mars is red and round
therefore
Some round thing is coloured
The premise and conclusion are matters of fact,
so is this “reasoning concerning matter of fact”?
10
– Is the inference merely “probable”? No!
– Does it go beyond “relations of ideas”? No!
– Does justifying the inference require any appeal to
experience or to causal relations? No!
– So Hume (if he were to consider any example of this
type) would have to count it as demonstrative.
“Demonstrative” => a priori?
But this is controversial: many Hume interpreters
have claimed that he counts an inference as
“demonstrative” only if its premise(s) – and hence
its conclusion – are a priori. Consider …
– “Were [any matter of fact] demonstratively false, it
would imply a contradiction, and could never be
distinctly conceived by the mind.” (E 4.2)
– “whatever is intelligible, and can be distinctly
conceived, implies no contradiction, and can never be
proved false by any demonstrative argument or
abstract reasoning à priori.” (E 4.18)
11
Is Demonstrative Reasoning
Limited to Mathematics?
“It seems to me, that the only objects of the
abstract sciences or of demonstration are quantity
and number, and that all attempts to extend this
more perfect species of knowledge beyond these
bounds are mere sophistry and illusion.” (E 12.27)
But Hume’s account of this limit is in terms of the
relative clarity of mathematical and moral ideas.
So if we want to find a posteriori demonstrative
arguments of any complexity, we have to look to
applied mathematics …
12
Hume on Applied Mathematics
Hume’s most explicit discussion of “mixed
mathematics” is in Enquiry Section IV:
– “it is a law of motion, discovered by experience,
that the moment or force of any body in motion is
in the compound ratio or proportion of its solid
contents and its velocity; and consequently, that
a small force may remove the greatest obstacle
. . . if, by any contrivance . . . we can encrease
the velocity of that force, so as to make it an
overmatch for its antagonist.” (E 4.13)
13
The momentum of a body is equal to its mass
multiplied by its velocity.
In any collision the total momentum of the colliding
bodies (in any given direction) is conserved.
Before …
25,000 m/s
4 m/s
2 kg
10,000 kg
After …
14
“Geometry assists us in the application of this
law . . . but still the discovery of the law itself is
owing merely to experience, and all the abstract
reasonings in the world could never lead us one
step towards the knowledge of it.” (E 4.13)
“Mathematics, indeed, are useful in all
mechanical operations . . . But ’tis not of
themselves they have any influence. . . .
Abstract or demonstrative reasoning . . . never
influences any of our actions, but only as it
directs our judgment concerning causes and
effects.” (T 2.3.3.2)
15
“No Matter of Fact is Demonstrable”
Let proposition P be: “All crows are black.”
– Suppose I say:
“P is demonstrable.”
Ridiculous, you would say! How can I possibly
claim to demonstrate that all crows are black?
– “Well”, I reply, “here’s my demonstration”:
1. All birds are black.
2. All crows are birds.
 All crows are black.
– That’s a demonstrative argument, isn’t it?
16
“Demonstrate” = “Deductively Prove”
When we say “P is demonstrable” (or “P is
deductively provable”), we don’t just mean:
– “Some deductively valid argument or other can
be found which has P as a conclusion.”
Instead, we mean something like:
– “P can be proved using some deductively valid
argument, from premises that we know with
absolute certainty to be true.
– So it is no surprise at all to find Hume stating
that “no matter of fact can be demonstrated”.
17
Humean “Demonstration”
In short, an argument is “demonstrative” if it
is deductively valid (in the informal sense:
its premises logically entail its conclusion).
– Useful examples of such argument occur
mostly in mathematics, pure or applied,
because mathematical ideas are precise
enough to allow complex trains of inference.
– One matter of fact can be demonstrated from
another, but no matter of fact can be
demonstrated tout court (i.e. a priori).
18
UP: The Uniformity Principle
In the Treatise
– “If reason determin’d us [to infer B from A], it
wou’d proceed upon that principle, that instances
of which we have had no experience, must
resemble those of which we have had
experience, and that the course of nature
continues always uniformly the same.” (T 1.3.6.4)
– This seems conditional: IF reason is involved,
THEN it must be based on this principle.
– But the principle seems implausibly strong.
19
The Uniformity Principle (2)
In the Enquiry
– “all our experimental conclusions proceed upon
the supposition, that the future will be
conformable to the past”. (E 4.19)
– No suggestion of conditionality (cf. also E 5.2:
“in all reasonings from experience, there is a
step taken by the mind” corresponding to UP).
– More vague than UP in Treatise, and so more
plausible: we expect the future to “resemble”
(E 4.21) the past, but not copy exactly.
20
The Uniformity Principle (3)
UP is Implicit, not Explicit
– Hume is not suggesting, even in the Enquiry,
that we think of UP explicitly when making
inductive inferences (cf. T 1.3.8.13).
– Rather, in making an inductive inference, we
manifest the assumption of UP, in basing our
inferential behaviour on past experience.
– Compare: we manifest the ascription of
causal necessity between A and B, when we
infer from A to B (cf. T 1.3.6.3 above).
21
A Sketch of the Argument
Part (i)
– Concludes that all factual inferences to the
unobserved are founded on experience.
Pivot
– Hence all factual inferences to the unobserved
are founded on UP.
Part (ii)
– But UP has no rational foundation.
– So factual inference is not founded on Reason.
22
The Part (i) Argument
Factual inference is founded on causation
– Causation is the only relation that enables us
to infer from one thing to another.
All knowledge of causal relations is
founded on experience
– A priori, we can know nothing of causation.
The “Founded on” Relation is Transitive
– i.e. if x is founded on y, and y is founded on z,
then it follows that x is founded on z.
23
The Pivot
All factual inference is founded on
experience.
All inference from experience is founded
on the Uniformity Principle.
– Because it requires that we extrapolate from
our experience, on the basis that what we
have not yet experienced will be similar.
Hence all factual inference is founded on
the Uniformity Principle.
24
The Part (ii) Argument
In Treatise I iii 6
– “let us consider all the arguments, upon which
[UP] may be suppos’d to be founded; … these
must be deriv’d either from knowledge [i.e.
demonstration] or probability”. (T 1.3.6.4)
– We can conceive a change in the course of
nature, so UP cannot be demonstrably true.
– Probable reasoning must be causal, and so
founded on UP. Hence it cannot itself provide
a foundation for UP, on pain of circularity.
25
Enquiry IV Part (ii)
Four “Kinds of Evidence”
– “It is common for Philosophers to distinguish
the Kinds of Evidence into intuitive,
demonstrative, sensible, and moral”. (Letter
from a Gentleman, 1745, p. 22)
– In the Enquiry, Hume argues explicitly that UP
cannot be founded on what we learn through
the senses, nor on intuition.
– Hence he rules out all four “kinds of evidence”,
not just demonstrative and probable inference.
26
A Sceptical Argument
All this seems to imply that Hume’s
argument is genuinely sceptical.
– It starts by showing that all factual inference is
founded on the Uniformity Principle;
– Then goes on to undermine every possible
rational foundation for UP;
– Then draws from this the conclusion that
factual inference has no rational foundation.
– This way of arguing does not make sense
unless the argument has sceptical intent.
27
The Gap in Hume’s Argument
The Uniformity Principle is not founded on:
– demonstrative argument
because a change in the course of nature is
possible, whereas any demonstrative argument
would have to yield total certainty;
– probable argument
because any probable argument is itself founded on
experience and hence on the Uniformity Principle.
But what if we could find a way of arguing
probabilistically but a priori?
28
– Hume just assumes this to be impossible.
Deductivist Interpretations
Antony Flew and David Stove
– Interpret Hume as a deductivist, who just
takes for granted that any argument which is
less than certain is therefore useless.
Tom Beauchamp, Annette Baier etc.
– Interpret Hume as an anti-deductivist, whose
argument proceeds from deductivist
assumptions, but whose ultimate point is to
undermine deductivism by showing its inability
to provide any basis for factual inference.
29
“Mediums” and Deductivism
When Hume says a “medium” is needed to
prove UP (he doesn’t speak of UP as itself a
medium), he need not be presupposing a
deductive paradigm of inference:
– Arguments do not always need a “medium” to
get from premiss to conclusion (e.g. T 1.3.7.5n).
– Even when they have one, that “medium” can
be merely “probable” (Dialogues 143).
– Hume sees that inductions are incurably fallible
even if nature is uniform (e.g. T 1.3.15.11).
30
Refuting Deductivist Interpretations
Why Canvass a Probable Argument for UP?
– On the deductivist and anti-deductivist
interpretations, Hume’s canvassing of a
“probable” foundation for UP makes no sense –
on deductivist principles, no merely “probable”
argument can provide a foundation for anything.
The Balance of Hume’s Scepticism
31
– Hume does appear to view his argument as
genuinely sceptical, but he certainly doesn’t
proceed on deductivist assumptions elsewhere:
indeed he is a strong advocate for induction.
Is Hume an Inductive Sceptic?
Does Hume deny that inductive inference
is founded on any sort of rational insight
into why nature should be uniform?
– YES!
Does Hume think that all inferences about
“matter of fact” are equally hopeless, so
that there’s no rational ground for
preferring one to another?
– NO!
32
The “No Argument” Interpretation
Don Garrett and Harold Noonan
– Garrett (1997) and Noonan (1999) claim that
Hume is only concerned to show that
inductive inferences are not caused by
argument, i.e. that there is no process of
ratiocination that leads us to infer inductively.
David Owen
– Owen (1999) claims that Hume is only ruling
out inference by intermediate steps, what he
understands by Lockean “reason”.
33
Refuting Garrett and Owen (1)
According to Garrett and Owen, “reason”
for Locke and Hume means quite
specifically our faculty of inference, a subfaculty of “the understanding”.
But this seems wrong (see slides 37-48):
– Writers of the time all seem to have used
“reason” and “the understanding” equivalently.
– They apparently meant to refer to a general
faculty of rational perception rather than a
more specific faculty of inference.
34
Refuting Garrett and Owen (2)
The Logic of the Part (ii) Argument
– Hume’s Part (ii) argument makes no sense on
the Garrett/Owen reading:
UP plays a role in the causation of factual inference;
UP is not itself caused by a process of raticination;
Therefore inductive inference is not caused by any
process of ratiocination
– This is a complete non-sequitur. Inductive
inference could be caused by a process of
ratiocination that involves UP!
35
Refuting Garrett and Owen (3)
Causation by Argument, or Foundation in
Reason?
– If Hume were only concerned to prove that
ratiocination plays no role in the causation of
induction (i.e. factual inference), then:
His argument would be incomplete, because he
does nothing to rule out the possibility that induction
could be caused by bad argument.
Much of his Enquiry argument would be redundant,
as he would have no need to refute the idea that
induction is founded on intuition or sensation.
36
Is Lockean Reason Inferential?
Don Garrett (1997):
– “‘Reason’, according to Locke, is the faculty of
the ‘discovering and finding out of Proofs’, ‘laying
them in a clear and fit Order’, ‘perceiving their
Connexion’, and ‘making a right conclusion’
(ECHU IV.xvii.3). Reason is thus a faculty of
finding, presenting, appreciating, and being
moved to belief by arguments. …” (pp. 26-7)
– “for Locke, ‘reason’ is simply the inferential or
argumentative faculty of the mind.” (p. 85)
37
Is Humean Reason Inferential?
Don Garrett (1997):
– “Similarly for Hume, reason is the faculty of
reasoning: of making inferences, or providing,
appreciating, and being moved by
arguments.” (p. 27)
David Owen (1999):
– “Hume sometimes uses ‘understanding’ and
‘reason’ as synonyms, though strictly
speaking the understanding is a more
inclusive faculty than reason.” (p. 142)
38
Locke on Reason as Inference
“The greatest part of our Knowledge depends upon
Deductions and intermediate Ideas: And in those
Cases [where we achieve only probability rather
than knowledge] we have need to find out, examine,
and compare the grounds of their Probability. In
both these Cases, the Faculty which finds out the
Means, and rightly applies them to discover
Certainty in the one, and Probability in the other, is
that which we call Reason.”
(Essay IV xvii 2)
See also Essay IV xvii 14, IV xx 16.
39
Locke on Reason as Intellect
“The Word Reason … stands for a Faculty in Man,
That Faculty, whereby Man is supposed to be
distinguished from Beasts, and wherein it is evident he
much surpasses them.” (Essay IV xvii 1, cf. IV xix 4)
“Nothing that is contrary to, and inconsistent with the
clear and self-evident Dictates of Reason, has a Right
to be urged, or assented to, as a Matter of Faith …”
(Essay IV xviii 10)
“But if they know it to be a Truth, they must know it to
be so either by its own self-evidence to natural
Reason; or by the rational Proofs that make it out to be
so.” (Essay IV xviii 11)
40
Locke on Reason as Perception (1)
“we … looke for noe greater certainty then what our
eyes can afford us, the whole evidence of this
assureance being noe more then what the word
Demonstration doth naturaly import; which is to
shew any thing as it is & make it be perceived soe
that in truth what we come to know this way is not by
proofe but intuition, all the proofe that is used in this
way of knowledg being noe thing else but shewing
men how they shall see right … without useing
arguments to perswade them that they are soe”
(Draft B of Locke’s Essay, 1671, p.153)
41
Locke on Reason as Perception (2)
“Inference … consists in nothing but the Perception of the
connexion there is between the Ideas, in each step of the
deduction, whereby the Mind comes to see, either the
certain Agreement of Disagreement of any two Ideas, as
in Demonstration, in which it arrives at Knowledge; or their
probable connexion, on which it gives or with-holds its
Assent, as in Opinion. … For as Reason perceives the
necessary, and indubitable connexion of all the Ideas or
Proofs one to another, in each step of any Demonstration
that produces Knowledge; so it likewise perceives the
probable connexion of all the Ideas or Proofs one to
another, in every step of a Discourse, to which it will think
Assent due. …” (Essay IV xvii 2).
42
Locke’s Scepticism about Faculties
Locke ridicules the language of faculties as a source of
philosophical error, and declares himself inclined to
forego it completely were it not that faculty words are
so much in fashion that “It looks like too much
affectation wholly to lay them by” (Essay II xxi 17-20).
When we refer to man’s “understanding”, all we can
properly mean is that man has a power to understand.
It is a serious mistake to speak of our faculties “as so
many distinct Agents”.
“the understanding, or reason, whichever your lordship
pleases to call it …” (First Letter to Stillingfleet, III 70)
43
Hutcheson on the Faculties
“Writers on these Subjects should remember the
common Division of the Faculties of the Soul. That
there is 1. Reason presenting the natures and
relations of things, antecedently to any Act of Will or
Desire: 2. The Will, or Appetitus Rationalis, or the
disposition of Soul to pursue what is presented as
good, and to shun Evil. … Below these [the Antients]
place two other powers dependent on the Body, the
Sensus, and the Appetitus Sensitivus, in which they
place the particular Passions: the former answers to
the Understanding, and the latter to the Will.”
Illustrations upon the Moral Sense (1728), SB §450
44
Price on Reason and Sense
“The power, I assert, that understands; or the faculty
within us that discerns truth, and that compares all the
objects of thought, and judges of them, is a spring of
new ideas. … Sense presents particular forms to the
mind; but cannot rise to any general ideas. It is the
intellect that examines and compares the presented
forms, that rises above individuals to universal and
abstract ideas. … Sense sees only the outside of
things, reason acquaints itself with their natures. …
Feeling pain, for example, is the effect of sense; but the
understanding is employed when pain itself is made an
object of the mind’s reflexion … “
A Review of the Principal Questions in Morals (1758), SB §590-2
45
Price on Reason as Perception
“In a word, it appears that sense and understanding
are faculties of the soul totally different: … The one
not discerning, but suffering; the other not suffering,
but discerning; and signifying the soul’s Power of
surveying and examining all things, in order to judge
of them; which Power, perhaps, can hardly be better
defined, than by calling it, in Plato’s language, the
power in the soul to which belongs … the
apprehension of Truth.”
A Review of the Principal Questions in Morals (1758), SB §593
46
Butler on Reason
Joseph Butler too identifies “reason” with
“the understanding”, and views it as
essentially perceptual:
“… as speculative reason may be neglected,
prejudiced, and deceived, so also may our
moral understanding be impaired and
perverted … This indeed proves nothing
against the reality of our speculative or
practical faculties of perception …”
Analogy of Religion (1736), Part I Chapter vi §19
47
Hume on Reason
Hume also identifies “reason” with “the
understanding”, and views it – initially at
least – as an essentially perceptual faculty,
contrasted with “the imagination”.
48
– For more on this, see §2 of Peter Millican,
“Hume’s Sceptical Doubts Concerning
Induction”, chapter 4 of Reading Hume on
Human Understanding (OUP, 2002).
– After Hume has proved that inductive inference
depends on “the imagination”, the terminology
gets a bit more complicated (op. cit. §2)
Hume’s ‘Sceptical Solution’
Hume sums up his sceptical conclusion
about the foundation of induction thus:
‘we … conclude … that, in all reasonings from
experience, there is a step taken by the mind,
which is not supported by any argument or
process of the understanding’ (E 5.2)
He then goes on:
‘If the mind be not engaged by argument to make
this step, it must be induced by some other
principle of equal weight and authority …’
49
Custom or Habit
Hume gives the principle a name, but makes no
pretence to understanding its ultimate basis:
‘This principle is CUSTOM or HABIT. By employing that
word, we pretend not to have given the ultimate reason
of such a propensity. We only point out a principle of
human nature, which is universally acknowledged, and
which is well known by its effects. Perhaps, we can
push our enquiries no farther, or pretend to give the
cause of this cause; but must rest contented with it as
the ultimate principle, which we can assign, of all our
conclusions from experience. ’ (E 5.5)
50
Why Rely on Custom?
Is custom a principle we should rely on? The very
question is pre-empted by our animal nature:
‘[Belief arising from inference through custom] is the
necessary result of placing the mind in such
circumstances. It is an operation of the soul, when
we are so situated, as unavoidable as to feel the
passion of love, when we receive benefits; or hatred,
when we meet with injuries. All these operations are
a species of natural instincts, which no reasoning or
process of the thought or understanding is able, either
to produce, or to prevent.’ (E 5.8)
51
The Irresistibility of Custom
In the Treatise also, Hume had appealed to the
irresistibility of custom:
‘Nature, by an absolute and uncontroulable
necessity has determin’d us to judge as well as to
breathe and feel; nor can we any more forbear
viewing certain objects in a stronger and fuller light,
upon account of their customary connexion with a
present impression, than we can hinder ourselves
from thinking as long as we are awake, or seeing
the surrounding bodies, when we turn our eyes
towards them in bright sunshine.’ (T1.4.1.7)
52
A Problem
However an appeal to irresistibility, as a
basis for assent, leaves Hume open to the
risk that his opponent will make the same
appeal on behalf of a different principle, e.g.:
‘I just find myself unable to resist belief in God,
and I’m as rational in this belief as you are in
your reliance on custom!’
If custom is just a principle of the imagination
rather than reason, how can Hume respond?
53
The ‘Antient Philosophers’
Hume raises this issue himself after discussing the
‘antient’ philosophers’ reliance on dubious
principles of the imagination (notably animistic
reading of intentions into nature, such as ‘horrors of
a vacuum’ etc.):
‘But here it may be objected, that the imagination,
according to my own confession, being the ultimate
judge of all systems of philosophy, I am unjust in
blaming the antient philosophers for makeing use of
that faculty, and allowing themselves to be entirely
guided by it in their reasonings.’ (T 1.4.4.1)
54
‘In order to justify myself, I must distinguish in the
imagination betwixt the principles which are permanent,
irresistable, and universal; such as the customary transition
from causes to effects, and from effects to causes: And the
principles, which are changeable, weak, and irregular; such
as those I have just now taken notice of. The former are
the foundation of all our thoughts and actions, so that upon
their removal human nature must immediately perish and
go to ruin. The latter are neither unavoidable to mankind,
nor necessary, or so much as useful in the conduct of life;
but on the contrary are observ’d only to take place in weak
minds, and being opposite to the other principles of custom
and reasoning, may easily be subverted by a due contrast
and opposition. For this reason the former are received by
philosophy, and the latter rejected.’ (T 1.4.4.1)
55
Justifying the Choice of Principles
Hume’s discussion in Treatise I iii 9-13 can
be seen as sketching an investigation into the
various belief-forming operations of the
imagination, identifying those that are reliable
(notably causal inference and appropriate
use of general rules) and those that are not
(e.g. caprice, credulity, indoctrination).
See my 1995 paper, ‘Hume’s Argument
Concerning Induction: Structure and
Interpretation’, §13, for more on all this.
56
Induction as Part of Reason
Having distinguished between the ‘established’
and the ‘trivial’ principles of the imagination,
Hume is happy to include the former within the
operations of ‘reason’:
It has been observ’d, that reason, in a strict and
philosophical sense, can have an influence on
our conduct after only two ways: Either when it
excites a passion by informing us of the
existence of something which is a proper object
of it; or when it discovers the connexion of
causes and effects, so as to afford us means ...
(T 3.1.1.12, cf. T 1.3.8.13, T 2.3.3.2)
57
Redefining ‘Reason’
In general we may observe, that as our assent to all
probable reasonings is founded on the vivacity of ideas, it
resembles many of those whimsies and prejudices, which
are rejected under the opprobrious character of being the
offspring of the imagination. By this expression it appears
that the word, imagination, is commonly us’d in two
different senses; and tho’ nothing be more contrary to true
philosophy, than this inaccuracy, yet in the following
reasonings I have often been oblig’d to fall into it. When I
oppose the imagination to the memory, I mean the faculty,
by which we form our fainter ideas. When I oppose it to
reason, I mean the same faculty, excluding only our
demonstrative
and probable reasonings. (T 1.3.9.19n)
58
Rationality in the Enquiry
In the Enquiry Hume’s discussion of rational
belief is less extensive.
His main emphasis seems to be on what Noxon
has called ‘methodological consistency’: custom
is our primary belief-forming mechanism, so our
beliefs in general should be judged by their
consistency with the results of custom.
See my 2002 book Reading Hume on Human
Understanding (OUP), pp. 161-9 and 437-41 for
more on all this.
59
Philo in the Dialogues
To whatever length any one may push his speculative principles of
scepticism, he must act, I own, and live, and converse like other
men; and for this conduct he is not obliged to give any other reason
than the absolute necessity he lies under of so doing. If he ever
carries his speculations farther than this necessity constrains him,
and philosophises, either on natural or moral subjects, he is allured
by a certain pleasure and satisfaction, which he finds in employing
himself after that manner. He considers besides, that every one,
even in common life, is constrained to have more or less of this
philosophy; that from our earliest infancy we make continual
advances in forming more general principles of conduct and
reasoning; that the larger experience we acquire, and the stronger
reason we are endowed with, we always render our principles the
more general and comprehensive; and that what we call philosophy
is nothing but a more regular and methodical operation of the same
kind. To philosophise upon such subjects is nothing essentially
different from reasoning on common life; and we may only expect
greater stability, if not greater truth, from our philosophy, on account
of its exacter and more scrupulous method of proceeding. (D 134)
60