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The Story of Scepticism


In common use ‘scepticism’ means a tendency to disbelieve or at least suspend belief in what you’re being told. But in philosophical circles it primarily means the tendency to disbelieve the evidence of the senses, or we might say, to not believe what we commonly take to be true about the world from our experience of it. In other words, is how things appear to us to be the same as they really are, or is reality itself radically different from its appear­ance?


Parmenides & Zeno

Let’s first go to Parmenides (515-450 BC), who was a Greek living in Elea in Southern Italy. Parmen­ides’ view was that change is an illusion, and thus our whole experience of reality is false.

To paraphrase his argument, Parmenides claimed that all is Being, since non-Being does not exist. But whence change, since to move from complete Being to complete Being is no move at all, no change? That is to say, the only change that can be made in absolute Being is by admit­ting not-Being into Being. However, not-Being does not exist. Therefore it’s imposs­ible for Being to change. Therefore all change is an illusion.

A different argument about the illusory nature of change and so the world we experience was advanced through a number of paradoxes by a pupil of Parmenides, Zeno (490-430 BC). To choose just one from Zeno’s many paradoxes of motion, let’s look at Achilles and the Tortoise.

This paradox has Achilles and the Tortoise in a race. Achilles, the fastest runner in Greece, has the virtue of being a good sport, and so gives the Tortoise a head-start of several cubits. Zeno’s argument is that it is impossible for Achilles to ever catch up with the Tortoise. Consider, while Achilles crosses the twenty cubits to where the Tortoise first started out, the Tortoise has moved on, let’s say, one cubit (it is a fast Tortoise). And when  Achilles has crossed that, the Tortoise has moved on, a further inch or so. And so on. And although the gap becomes diminishingly small, the Tortoise is always ahead, and Achilles can never catch up with him.

Your reaction to this might be the same as that of many of those who originally heard it: to laugh derisively and snort, “Everybody knows that a fast runner can quickly overtake a tortoise! What nonsense is Zeno speaking?” But this is, I think, to miss Zeno’s point. Zeno is questioning how motion specifically, or change generally, can be possible, given his arguments. What’s wrong with the argument?

Aristotle provided a good answer to this question, in which he prefigured quantum mechanics by over two thousand years. He said that space is only potentially and not actually infinitely divisible. Or, because a line cannot be infinitely divis­ible or composed of dimensionless points, only finite divisions of space can be real. In a modern idiom, space is quantised.



I think it’s fair to say that in the Classical world a view of the distinction between experience and reality reached its highest expression in the philosophy of Plato (427-347 BC).

Plato’s idea was to say that there is an eternal real­ity independent of the world of everyday experience, in which exist the perfect Forms or Ideas of things. Since they are perfect and unchanging, these things are the true reality, they have true Being, whereas this world of change is an illu­sion.

A good way to think of Forms is as ideals, or perhaps paradigms, that is, like perfect blueprints from which all the things in this world fall short. For instance there would be a Form of Table, an abstract ‘Table’ blueprint, which all tables would be imperf­ect instances of.

There are many problems with the theory of Forms, some of which Plato acknowledged. What would the idea of a perfect Table be – or of Cat, of Rat, or of Disease? Surely the idea of ‘perfection’ differs according to the use to which something is to be put. A perfect Disease would presum­ab­ly be imm­une to every Cure, whereas a perfect Cure would cure every Disease! However, the theory an attempt to syst­em­­atic­ally think through how change and being can coexist, while showing that experience is not a good guide to reality. In this way, it’s the height of Greek scepticism.

Plato’s view of the relationship between experience and reality is exemplified in the Allegory of the Cave, found in his dialogue the Republic. Humanity is like prisoners in a cave chained up to face a wall. Behind us is a walkway along which people and things pass, and their shadows are cast on the wall in front of us by means of a fire. Because we have never experienced anything else, we mistake the shadows we see for the real thing; and when we hear the echoes of voices in the cave, we think it’s the shadows talking. For Plato, seeing the truth about the ideal Forms is like escaping from the chains, first to turn to see the real things that cast the shadows, and then eventually to ascend out of the cave finally to the full light of day.


The Sophists & Pyrrhonians

The Sophists were active around the time of Socrates. These thinkers doubted it was possible to get real know­ledge since they believed that all truth was relative to the individual. A wind that felt warm to someone could feel cold to someone else, for instance. Protagoras is famous for saying that ‘man is the measure of all things’, and Gorgias said that ‘nothing exists, and if it did, no-one could know it, and if they knew it, they could not commun­ic­ate it.’ So instead of seeking truth, the Sophists focused on winning argu­ments, especially in law courts, and how to be happy and successful in life.

There was also a school of scepticism named after Pyrrho (360-270 BC). The Pyrrhonain school was radically scept­ic­al, claiming that we cannot know anything, since arguments also have contrary arguments. If you asked them if they know that we can know nothing, they would answer ‘no’. They advocate rather a ‘suspension of belief’.

Pyrhho himself claimed that because all knowledge involved uncertainty we could not know that one course of action was actually better than another, so, for instance, you might as well follow the customs of your surroun­dings, whatever your actual beliefs. Pyrrho’s disciple Timon (died 235 BC) went about as far as scepticism can go, and argued that you can’t even prove the princip­les of logic, that is, of rational argument. Rather, finding the roots of any argument would require either an end­less chain of reasoning, or circular reason­­ing, so no argument can be ultimately justified. Timon’s Pyrrho­nain successors then tended to demonstrate their scepticism, that is, the uncertainty of all knowledge, by arguing vigorously for both sides of an issue.



Let’s skip forward two thousand years or so, to René Descartes (1596-1650), who is called ‘the father of modern philosophy’ just because of his sceptical approach. You’ll know Descartes’ founda­tional thought, ‘cogito ergo sum’ – ‘I think therefore I am’; but let me put this infamous first step of modern philosophy a little in context.

Descartes believed that Galileo had not provided adequate philosophical foundations for science. As he reports in his Discourse on Method of 1637,  in 1619 he had a vision of a new science, or more precisely a vision of a way of unifying the sciences. Descartes stated the first precept of his Method in the Discourse on Meth­od thus: “never to accept anything as true if I did not have evident know­ledge of its truth.” This has become known in Cartesian circles as ‘The Method of Doubt’.

The use of this method was emphasised by Descartes’ in his Meditations (1642) through the possibility that for all he knows he’s dreaming, or the possibility of there being an evil demon who systematic­ally deceives him about everything. How does he know that either possibility is not the case, and so how does he know that what he thinks is true about the world he perceives is true, even the very existen­ce of material objects? As he says, “there is nothing in all that I formerly believed to be true, of which I cannot in some measure doubt.”

This is the context in which he argues that no matter how badly he is being deceived, in being deceived he neverthe­less has thoughts, and in having thoughts, he must exist: ‘I think therefore I am’. This argument then pro­vides the first step away from radical doubt, Descartes claims.

However, Descartes might have asked himself a question any later Witt­gen­steinians might also want to ask them­selves,  ‘How can I be sure that the words mean what I think they do; especially as I can’t rely on my exper­ience of the world to validate them?’ Or a Buddhist might object that Descartes has presupposed the self, the I, in his first thought, and that a better formu­lation of his indubitable truth might be ‘there is thought, therefore there is being’.

Descartes’ route out of his sceptical hole of doubt of all that is not incontrovertible used some not very incontrovertible ‘proofs’ of the existence of God, allied with equally dub­ious arguments about what we can assume about God’s desire not to deceive us. In particular, Descartes argued that it would be inconsist­ent with the goodness of God for Him to deceive us by pre­senting us with ideas of a material world with no material world corres­ponding to them.



In his book A Treatise Concerning Human Nature, David Hume (1711-1776) is famously sceptical about causation. His argument about this was that although we frequently see one thing following another, we do not see or have any other impression of cause itself. Rather, through repetitive experience we come to associate one type of thing as always happening after another, and thus come to infer the idea of the first thing causing the second. But we don’t see the cause. So, there’s no reason to believe in causation.

This scepticism about causation only worked for Hume because he didn’t have access to modern science, with its system­atic ideas of how one thing causes another at the subatomic level. The fact that we know causes through analysis not experience is a problem only if we have Hume’s reliance on experience. But we would say that we believe things to exist that we could never possibly experience. In this case, I think Hume was insufficiently sceptical about his own theory of knowledge.



In modern philosophy the experience/­reality distinction is best formul­ated by Immanuel Kant (1724-1804). Kant thought our experience of the world is constructed through faculties he called ‘Categories’. The Categ­ories are fundamental aspects of mental operation which predetermine how a rational mind will organize its experience. For instance, Kant reasonably cl­a­ims that our minds construct our experience of the world in accord­ance with the Categories of space and time. The Categories include other features of our experience, such as causality. Thus, Kant thinks that causality is a feature of the world of appearances, and not of the world as it is in itself. I think he’s wrong about this, and causality is an aspect of the world independent of our experience of it.

However, I would relate Kant’s thinking to the neuroscientific theory that our experience of the world is constructed in our brains from information received via our nerves. So the appearance of things to us is very much a product of a particularily human way of experiencing the world. We might then ask, how is the experience different from reality itself? This brings us right back to the scepticism that began with Parmenides.

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