Let us just note that legitimate forms of argument must use the following forms:
(1) Deduction, yielding necessary truth (e.g., various types of syllogism)One should note that “inference to the best explanation” is frequently considered a form of inductive argument, but some classify it as a sui generis form of reasoning. Whatever the classification one choices, however, the fact remains that it is (1) an important and legitimate form of reasoning and (2) firmly in the same general category as induction as a method of argument that yields non-necessary truth.
(2) Induction, yielding probable truth, and further divided into(1) induction by simple enumeration;(3) Inference to the best explanation/abduction, yielding probable truth.
(2) inductive argument by analogy;
(3) statistical syllogism, and
(4) induction to a particular.
The idealist and indeed the realist can appeal to direct personal experience as a posteriori evidence of the following:
Proposition 1: the only things I have direct and immediate experience of areSo from this the idealist can establish a posteriori the following proposition:(i) my own mind, and
(ii) ideas that are presented to the mind, further divided into(a) ideas over which I have control (imaginations, thoughts expressed in language, etc.) and
(b) ideas over which I have no control (some perceptions of the senses).
There exist ideas in my mind over which I have no control (perceptions of the senses).But, furthermore, the idealist or realist can continue and construct an inductive argument, to support the idea that other minds exist.
To do this, an inductive argument by analogy can be used, and such arguments have the following general form:
a, b, c, d all have the properties P and QTherefore we can construct the following argument:
a, b, c all have the property R
Therefore d probably has the property R
where a, b, c, d are things or events, and P, Q, and R are properties of the former things.
“a, b, c, d, … n have the properties P, Q, R, SOf course, you could extend the analogy to every person you meet and strengthen the argument, but the induction by analogy is clear: it is probable that the humans we experience who claim to have other minds really do have conscious minds in the same way any individual person who experiences consciousness directly does.
a has the property of T
Therefore b, c, d, … n probably have the property of T,”
where a = myself
b = a thing that appears to be a person with a mind
c = a second thing that appears to be a person with a mind
d = a third thing that appears to be a person with a mind, etc. to
n = 14th thing that appears to be a person with a mind.
P = speaks language,
Q = seems to have emotions
R = responds to pain
S = can report descriptions of objects seen
T = a conscious mind.
Note that this inductive argument has no necessary truth: it has only probable truth, and certainly does not exhaust the list of possible explanations for our experience of things that claim to be minds like us.
For example, the idealist is also subject to the Cartesian evil demon argument: how can the idealist know that all his perceptions of objects he cannot control are not caused by some malevolent force that is deceiving him? After all, he has already given an inductive argument that it is probable that other minds exist, but that argument has no necessary truth. It might be that only some of the things that claim to be other minds really have minds, or that there are only two minds: myself and the evil demon.
We could list other possible reasons:
(1) an evil demon is deceiving me;This does not exhaust the possibilities. You can construct increasingly outlandish ones that nevertheless might be possible as long as they are at least logically possible.
(2) I do have a single mind, but I am dreaming or hallucinating all other minds (by some process internal to my mind that I do not understand), and other minds do not exist.
(3) I am some entity like a “brain in a vat” whose consciousness is given to me by some unknown minds for reasons unexplained.
So how can the idealist justify the view that his inductive argument by analogy is the best explanation of the things that seem like other minds, when such minds might not exist and be delusions? How can the idealist (or realist) answer the radical skeptic? This is not a trivial point, but a fundamental one.
It is at this point that we need to invoke the type of reasoning called inference to the best explanation (Harman 1965; Vogel 1990; Scruton 1994: 20), a form of induction or (alternatively) a legitimate non-deductive reasoning like induction.
That is, if you can provide good reasons why your theory offers a better and systemic explanation of the evidence, and show why the rival theories do not (or show that they explain very little at all), then you are rationally justified in choosing the theory that is the best explanation.
First, the evil demon. If the skeptic refuses to give reasons for why the demon caused experience x or y, or why the demon consistently causes us to have belief z, and says merely that the demon just causes them and nothing more, we already have a good reason for believing that the “demon theory” makes for a poor explanation. Even when ad hoc explanations are offered in response to such questions, things are not much better. By contrast, we can construct better explanations for so many experiences involving other minds using the theory that they exist and are not there to deceive us. We can even predict many types of behaviour of other minds based on our theory.
Furthermore, “demon theories” really do have no systemic explanation of why and how the demon deceives. After all, many experiences do not turn out to be obviously deceptive or inconsistent in the way you would expect if some force was really trying to deceive you.
Idea (3) above has less explanatory value than (1), for it openly admits that things happen for unexplained reasons.
If we move to (2) above, we can argue that dreams and hallucinations have different properties than what we call conscious, non-dreaming existence: dreams are usually more fragmented, less clear, and often inconsistent, and lack the constancy we find in “waking” conscious existence. Does the dreaming hypothesis offer a powerful explanatory theory for many aspects of the consistency of waking life, as compared with the hypothesis that waking consciousness contains other minds like ours? Not really.
By inference to the best explanation, one can argue that the behaviour, properties and consistency of our experience of other minds suggest that they do exist and other explanations are inferior on present evidence.
Note how, as we have seen, even the idealist must invoke a non-deductive inference to the best explanation to choose between competing theories and overcome the skeptics.
Now let us proceed to the next proposition that the idealist must accept:
“There are ideas over which I have no control with a causal origin external to me.”The idealist must accept this, as it follows on logically from his rejection of the sceptical “dreaming” theory above.
For it is possible that, although I exist as a real mind, my entire conscious life might be a dream generated by some internal process inside my mind that I do not understand. Why? The reason is that it is clear, by direct personal experience, that we do not understand many aspects of our cognition and thought (e.g., why do we make Freudian slips, or sometime forget things we easily remember on other occasions?). There is no reason a priori why our latter “dreaming” explanation is necessarily false.
So the idealist is committed to the view that some external cause is the explanation for those ideas over which we have no control (e.g., constant perceptions of the senses).
How does he provide a rational justification for this? Again, it is by inference to the best explanation: the other theories positing a mere unknown internal cause of the ideas over which we have control are judged to be inferior explanations.
We now have three propositions:
Proposition (1): There are ideas over which I have no control (perceptions of the senses).But notice how these propositions can be accepted by any realist too, who will have used the same type of arguments to defeat the Cartesian skeptic. It is at this point that the idealist and indirect realist part company.
Proposition (2): It is probable that the humans we experience who claim to have other minds really do have conscious minds in the same way any individual person who experiences consciousness directly does.
Proposition (3): There are ideas over which I have no control with a causal origin external to me.
For the question is now:
What is the external cause which is the causal origin of those ideas over which we have no control?Some of the earlier sceptical theories are still relevant. But the list of possible explanations or theories is larger.
If we have given an inductive argument for the probability of an external cause, then no logically possible external cause can be ruled out a priori.
Here the skeptic will demand that his theories at least be considered as possibilities, but also the theistic idealist, non-theistic idealist, realist and panpsychist will add other theories too:
(1) an evil demon is the external cause (skeptic);Other possibilities could be added of course, but these make a useful list.
(2) we are “brains in a vat” whose consciousness is given by some unknown minds for reasons unexplained (skeptic);
(3) a god of classical theism is the mind that is external cause (theistic idealist);
(4) a “super-mind” that is not the god of classical theism is the external cause;
(5) we live in a purely mental world, but every object of our perception is invested with a mind and hence there are multiple external causes for all constant objects we perceive (a variant on panpsychism);
(6) there are non-mental objective external objects that are the causal origin of our perceptions of them (indirect realist).
Can the idealist rule out any of these other possibilities a priori without simply begging the question by already assuming idealism is true? I do not think so.
All must be regarded as at least possibilities.
And at this point it is induction and inference to the best explanation that must be invoked to decide which one is true.
The idea that the indirect realist does not use legitimate logic or induction is untrue, for we need only consider the induction by analogy arguments that can be invoked by the realist or the idealist:
(1) the idealist:These are both inductions by analogy: in this step, the realist and idealist are on the same epistemological ground.
We observe directly things that claim to be minds that probably have minds (e.g., people). On analogy, there might be an unobserved super-mind that is the external cause.
(2) the realist:
We observe directly in our minds objects that appear to have no minds and probably do not have minds (e.g., tables, chairs, rocks, books). On analogy, there may be unobserved non-mental objects that are the external causal origin of our perceptions of these things.
But who is right? We now need to move beyond this to inference to the best explanation.
Does the idealist theory of the super-mind explain the vast set of experiences and evidence we see around us?
(1) what are fossils under the idealist theory? Presumably they are mere ideas that existed in the super-mind in the past.The questions that the idealist cannot give coherent answers to multiply to huge numbers quickly:
(2) but this just raises the question: why did the super-mind create in its thought a world 541 to 485 million years ago devoid of human minds with Cambrian aquatic animals and plants? To what purpose?
For some unexplained reason the super mind imagined all these animals. Then thought of the idea of “mass extinctions.” But then thought of vast numbers of new animals in later eras, only to cause more “mass extinctions” by its ideas. Why?
(1) did dinosaurs have minds?When pressed, there is little the idealist can say in response precisely because his theory has poor explanatory power. These questions remain mysterious puzzles.
(2) when did animals first have real minds? Did the “mass extinctions” cause suffering to animals if they had minds?
(3) why did the super-mind “destroy” the dinosaurs?
(4) why are some humans colour blind?
But, as I have shown in the last post, the indirect realist materialist has an interpretation of the natural sciences that has great explanatory power and can give coherent and powerful explanations of all these questions and thousands more, and is superior to the idealist theory.
The universe really exists as a material external world and requires no god or mind for its existence and operation. Nor will it do for the idealist to say that idealism just follows natural science in its explanation of the world but stripped of matter: for natural science says the universe is an independent entity and has autonomous natural laws that do not require any god or super-mind to create events and objects in it. That is the whole thrust of modern science since Newton!
All life on earth exists in an external world and evolved by Darwinian natural selection: the result of (1) chance mutation or combination of real DNA and (2) the deterministic process of survival of fitter animals.
DNA is a real external object that creates animals by genetics and biochemistry.
And of course once realism is accepted it is but a short step by inductive evidence to the probable conclusion that minds are causally dependent on brains.
There is a vast research literature about animal minds: they are dependent on the complexity of brains that really exist inside the organisms as external objects in the real world. We have a probable inductive theory about why the dinosaurs died out: a chance contingent event caused their destruction when an asteroid hit the earth. Precisely the type of chance event that can happen in a real external universe like ours with real asteroids flying around our solar system.
Human beings experience colour blindness because of genetic defects and disease, and so on, and so forth.
In short, an inference to the best explanation supports realist materialism as the most powerful explanatory theory. It is rational, powerful and supported by evidence.
Harman, Gilbert H. 1965. “The Inference to the Best Explanation,” Philosophical Review 64: 88–95.
Moser, Paul. 1990. “Two Roads to Skepticism,” in M. D. Roth and G. Ross (eds.), Doubting: Contemporary Perspectives on Skepticism. Kluwer, Dordrecht. 127–139.
Scruton, R. 1994. Modern Philosophy: An Introduction and Survey. Penguin Books, London.
Vogel, Jonathan. 1990. “Cartesian Skepticism and Inference to the Best Explanation,” The Journal of Philosophy 87.11: 658–666.