The Fabric of Reality David Deutch

part of myself, solipsism no longer has any argument against the validity of
such study, which is now defined as no more than a form of introspection.
Solipsism allows, indeed assumes, that knowledge of oneself can be
obtained through introspection. It cannot declare the entities and processes
being studied to be unreal, since the reality of the self is its basic postulate.
Thus we see that if we take solipsism seriously — if we assume that it is true
and that all valid explanations must scrupulously conform to it — it self-
destructs. How exactly does solipsism, taken seriously, differ from its
common-sense rival, realism? The difference is based on no more than a
renaming scheme. Solipsism insists on referring to objectively different
things (such as external reality and my unconscious mind, or introspection
and scientific observation) by the same names. But then it has to reintroduce
the distinction through explanations in terms of something like the ‘outer part
of myself.’ But no such extra explanations would be necessary without its
insistence on an inexplicable renaming scheme. Solipsism must also
postulate the existence of an additional class of processes — invisible,
inexplicable processes which give the mind the illusion of living in an
external reality. The solipsist, who believes that nothing exists other than the
contents of one mind, must also believe that that mind is a phenomenon of
greater multiplicity than is normally supposed. It contains other-people-like
thoughts, planet-like thoughts and laws-of-physics-like thoughts. These
thoughts are real. They develop in a complex way (or pretend to), and they
have enough autonomy to surprise, disappoint, enlighten or thwart that other
class of thoughts which call themselves ‘I.’ Thus the solipsist’s explanation of
the world is in terms of interacting thoughts rather than interacting objects.
But those thoughts are real, and interact according to the same rules that the
realist says govern the interaction of objects. Thus solipsism, far from being
a world-view stripped to its essentials, is actually just realism disguised and
weighed down by additional unnecessary assumptions — worthless
baggage, introduced only to be explained away.
By this argument we can dispense with solipsism and all the related theories.
They are all indefensible. Incidentally, we have already rejected one world-
view on these grounds, namely positivism (the theory that all statements
other than those describing or predicting observations are meaningless). As I

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remarked in Chapter 1, positivism asserts its own meaninglessness, and
therefore cannot be consistently defended.
So we can continue, reassured, with common-sense realism and the pursuit
of explanations by scientific methods. But in the light of this conclusion, what
can we say about the arguments that made solipsism and its relatives
superficially plausible, namely that they could neither be proved false nor
ruled out by experiment? What is the status of those arguments now? If we
have neither proved solipsism false nor ruled it out by experiment, what 
have
we done?
There is an assumption built into this question. It is that theories can be
classified in a hierarchy, ‘mathematical’ —> ‘scientific’ —> ‘philosophical’, of
decreasing intrinsic reliability. Many people take the existence of this
hierarchy for granted, despite the fact that these judgements of comparative
reliability depend entirely on philosophical arguments, arguments that
classify themselves as quite unreliable! In fact, the idea of this hierarchy is a
cousin of the reductionist mistake I discussed in Chapter 1 (the theory that
microscopic laws and phenomena are more fundamental than emergent
ones). The same assumption occurs in inductivism, which supposes that we
can be absolutely certain of the conclusions of mathematical arguments
because they are deductive, reasonably sure of scientific arguments
because they are ‘inductive’, and forever undecided about philosophical
arguments, which it sees as little more than matters of taste.
But none of that is true. Explanations are not justified by the means by which
they were derived; they are justified by their superior ability, relative to rival
explanations, to solve the problems they address. That is why the argument
that a theory is 
indefensible can be so compelling. A prediction, or any
assertion, that cannot be defended might still be true, but an explanation that
cannot be defended is not an explanation. The rejection of ‘mere’
explanations on the grounds that they are not justified by any 
ultimate
explanation inevitably propels one into futile searches for an ultimate source
of justification. There is no such source.
Nor is there that hierarchy of reliability from mathematical to scientific to
philosophical arguments. Some philosophical arguments, including the
argument against solipsism, are far more compelling than any scientific
argument. Indeed, every scientific argument assumes the falsity not only of
solipsism, but also of other philosophical theories including any number of
variants of solipsism that might contradict specific parts of the scientific
argument. I shall also show (in Chapter 10) that even purely mathematical
arguments derive their reliability from the physical and philosophical theories
that underpin them, and therefore that they cannot, after all, yield absolute
certainty.
Having embraced realism, we are continually faced with decisions as to
whether entities referred to in competing explanations are real or not.
Deciding that they are not real — as we did in the case of the ‘angel’ theory
of planetary motion — is equivalent to rejecting the corresponding
explanation. Thus, in searching for and judging explanations, we need more
than just a refutation of solipsism. We need to develop reasons for accepting
or rejecting the existence of entities that may appear in contending theories;
in other words, we need a criterion for reality. We should not, of course,
expect to find a final or an infallible criterion. Our judgements of what is or is

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not real always depend on the various explanations that are available to us,
and sometimes change as our explanations improve. In the nineteenth
century, few things would have been regarded more confidently as real than
the force of gravity. Not only did it figure in Newton’s then-unrivalled system
of laws, but everyone could feel it, all the time, even with their eyes shut —
or so they thought. Today we understand gravity through Einstein’s theory
rather than Newton’s, and we know that no such force exists. We do 
not feel
it! What we feel is the resistance that prevents us from penetrating the solid
ground beneath our feet. Nothing is pulling us downwards. The only reason
why we fall downwards when unsupported is that the fabric of space and
time in which we exist is curved.
Not only do explanations change, but our criteria and ideas about what
should count as an explanation are gradually changing (improving) too. So
the list of acceptable modes of explanation will always be open-ended, and
consequently the list of acceptable criteria for reality must be open-ended
too. But what is it about an explanation — given that, for whatever reasons,
we find it satisfactory — that should make us classify some things as real
and others as illusory or imaginary?
James Boswell relates in his 
Life of Johnson how he and Dr Johnson were
discussing Bishop Berkeley’s solipsistic theory of the non-existence of the
material world. Boswell remarked that although no one believed the theory,
no one could refute it either. Dr Johnson kicked a large rock and said, as his
foot rebounded, ‘I refute it 
thus.’ Dr Johnson’s point was that Berkeley’s
denial of the rock’s existence is incompatible with finding an explanation of
the rebound that he himself felt. Solipsism cannot accommodate any
explanation of why that experiment — or any experiment — should have one
outcome rather than another. To explain the effect that the rock had on him,
Dr Johnson was forced to take a position on the nature of rocks. Were they