Thomas Reid on ideas and our knowledge of the external world

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Maximillian Craig
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1 Thomas Reid on ideas and our knowledge of the external world inquiry into the human mind and the principles of commonsense, chapter 5, sections 7 and 8 Prof. Mark Steen Phil 112 Spring 2013

2 Commonsense philosophy Thomas Reid ( ) is the chief figure of the Scottish Commonsense School of Philosophy. This view (usually) favors the dictates of commonsense over the more wild doctrines of the philosophers, such as the beliefs that we do not know whether or not there is an external world and that we never directly perceive physical objects. If this is wisdom, let me be deluded with the vulgar.

3 To what purpose is it for philosophy to decide against common sense in this or any other matter? The belief of a material world is older, and of more authority, than any principles of philosophy. Also, we cannot get rid of commonsense. Reason...cannot throw [commonsense] off: if she will not be the servant of commonsense, she must be her slave...methinks, therefore, it were better to make a virtue of necessity...[and]...reconcile our reason to [the commonsense belief in the external world] as well as we can.

4 what leads to skepticism: the way of ideas Representational (or Indirect ) Realism is the view that we do not perceive external objects directly, rather, we perceive ideas /sense-data /images, or some kinds of mental items which are caused by external objects, which we only indirectly perceive. Everyone in the Early Modern period, and most Ancient philosophers, accepted this view of perception. One big problem, thinks Reid, is that once you accept that you never directly perceive physical, external, mind-independent objects, what good reason do we have for supposing there are any?

5 Two Pictures

6 Representational realist presupposition All R.Realists assume that, if there are any material objects, they must resemble (at least some of) our perceptions. We can conceive of nothing which is not like our ideas. But, no argument is given for it (since folks on all sides agreed). Why believe it? It seems to Reid that nothing could be more obvious than that no material object is like any idea at all. (Compare a Pegasus with the idea of a Pegasus - don t confuse the two, for Pegasus doesn t exist, but the Pegasus idea does. Pegasus is a horse with wings, but the idea of Pegasus isn t, although it does represent a horse with wings.) The notions of external physical objects is not optional--it must be part of our nature to have such ideas. (Reid thinks we get this idea neither by sensation nor reflection).

7 Further Problems With The Way of Ideas Berkeley/Hume etc. thought that material objects needed to be proved in order to be believed justifiably. But why think this? They must be operating on the general principle that (P) one should not believe anything except what can be proved by reasoning. But why believe P? Does it stand up to its own criteria? That is, can P be proven by reasoning? Also, belief in P entails that we should not believe anything, not even P. This is not so much the worse for knowledge or belief, but so much the worse for P.

8 it gets worse [People like Hume] appears to be but a half-skeptic...[i would like him to prove] the existence of his own impressions and ideas. No man ever did, or could offer any reason for this belief....i should be leave to know, why they believe the existence of their impressions and ideas. The true reason I take it to be, because they cannot help it; and the same reason will lead them to believe many other things. Reid s putting them in a dilemma: belief in impressions and ideas is either justified or not. If it is not justified, nothing is, and so we have no knowledge whatsoever. If it is justified, on the basis that we are unable to not believe it, then us non-skeptics or non-representationalrealists can justify our beliefs in material, mind-independent objects on the same basis--that we cannot help it.

9 Perhaps belief in material objects is axiomatic, or fundamental/basic. These are beliefs which justify, but are themselves not justified by any further beliefs.

10 problems for a berkeleyan argument for idealism 1. We can have no conception of the existence of anything but what resembles some sensation or idea in our minds. 2. Nothing outside of our minds could resemble any sensation or idea in our minds 3. So, we have no conception of the existence of material, mind-independent objects. 4. We should not believe in what we have no conception of (in fact, we cannot). 5. So, we should not believe in the existence of material, mind-independent objects. (in fact, we cannot). (1) is what Reid questions. It hasn t been proved, and is not at all self-evident, in fact it seems false. My idea of my wife does not resemble my wife at all.

11 Common Reidian methodology Philosopher S asserts P, which seems crazy. S asserts Q in argument for P. Q is semi-plausible. S then argues for the conditional : (Q -> P) Suppose you accept the conditional. But just because Q is semi-plausible and the conditional seems true doesn t mean you must accept P. If not-p is more plausible than Q, then you can equally argue that, since the conditional is true, and P is false, that Q must be false.

12 example - brain-in-a-vat Ibrahim says I don t know I have a hand. Ibrahim s argument is that: If I know that I have a hand, then I know (or come to know) that I m not a brain-in-a-vat. But, I don t know (nor can I come to know) that I m not a brain-in-a-vat, so I must not know that I have a hand. But Reid could say, I have much more confidence that I know I have a hand than I do that I do not know that I m not a brain-in-a-vat. So, I must know that I m not a brain-in-a-vat, or perhaps the conditional (If I know I have a hand, then I know (or can come to know) that I am not a brain-in-a-vat) is false. I have a higher credence in the falsity of the conditional and that I know I have a hand than I do in the proposition that I cannot know that I m not a brain-in-a-vat. So, it doesn t seem like a standard skeptical argument template works

Reid Against Skepticism

Reid Against Skepticism Thus we see, that Descartes and Locke take the road that leads to skepticism without knowing the end of it, but they stop short for want of light to carry them farther. Berkeley, frightened at the appearance