Ancient and modern scepticism in a nutshell.

There was a great deal of sceptical thought in ancient Greece before scepticism became a self conscious philosophical stance. Here are one or two examples.

Socrates and Plato contributed some significant elements to the development of sceptical thought, without themselves being full-blooded sceptics.

An academic sceptic is one who denies the possibility of knowledge.

A pyrrhonean sceptic is one whose doubts are universal and who therefore makes no claims to knowledge.

Michel de Montaigne, the seventeenth century metaphysical poets, and Bayle.

Positivist philosophy in its broadest sense is a general tendency in philosophy which embraces aspects of the thought of many philosophers including Humean scepticism, the work of Comte (who coined the term), elements of utilitarianism and pragmatism, and logical positivism.

The word "sceptic" comes from a Greek word which means "seeker after knowledge". It came to be used philosophically for those who sought but failed to find, and hence for those whose doubts, even about the possibility of knowledge, were extreme and pervasive. The term however, is also used in cases of more moderate or less general scepticism.

Sceptical doubts are to be found throughout the history of western philosophy, but philosophers whose philosophy was exclusively or primarily sceptical, and who are therefore called sceptics, appear during just one period in the philosophy of ancient Greece. This period begins in Plato's Academy after the death of Plato (348 BCE) with the "Academic Sceptics" and is taken up by Pyrrho of Elis (360-270 BCE) and runs through until comprehensively documented five centuries later by Sextus Empiricus (c. 160-210 CE).

In its most extreme form greek scepticism doubted that our experience of the world (or anything else) yielded any knowledge, all one could know was that things appear to be as they appear to be, "appearances appear". Not only do we not have any definite knowledge, according to the most extreme pyrrhoneans, but no proposition can be properly regarded as more probable than its negation. This yields the notion of "equipollence". It was an objective of some sceptics to demonstrate of any proposition allegedly known to be true, that it could not be known even to be more probable than its negation.

Such sceptics termed their opponents, those who were prepared to assert the truth of any proposition, "dogmatists".

In "modern" philosophy (i.e. since Descartes) the two most important kinds of sceptical thought are systematic doubt and positivism.

• Systematic doubt is the method used by Descartes, who so doubted the knowledge of his contemporaries that he thought it desirable to rase the entire structure to the ground and begin again with a clear slate. This is scepticism about received opinion as a prelude to the construction of a dogmatic philosophical system.
• positivism is another kind of limited scepticism which is married with a constructive program. In this case the most prominent element of the scepticism is scepticism about the senses, and the constructive element involves some conception of proper scientific method, often combined with the reformulation of scientific theories in phenomenalistic terms. These phenomenalistic reformulations may be seen as a modern variant of the pyrrhonean view that we can know only about appearances, not about anything we might suspect to be an external cause or subject of those appearances. The prototype of positivistic scepticism is David Hume, its first prophet Auguste Comte.

Possibly the earliest philosopher thought to have had sceptical leanings was Heraclitus, the instigator of that most elementary source of scepticism mistrust of the senses. Heraclitus believed that all is change and strife and that good and evil are one. He advocated introspection as a source of truth.

Zeno of Elea was a student of Parmenides who showed particular agility in finding rational arguments to support Parmenidian doctrines. Though his motivation seems to have been dogmatic rather than sceptical, his way of supporting Parmenidian doctrine seems primarily to have been by undermining the principle opposition, Pythagorean pluralism. He provides the clearest and most incisive early examples of a method which was to become the hallmark of Pyrrhonean scepticism, that of undermining a dogmatic opponents position by assuming it to be true and deductively deriving a contradiction. His most famous paradox is that of Achilles and the tortoise in which is argued that Achilles can never overtake the tortoise. As well as this (perhaps unintentional) contribution to the armoury of subsequent sceptics, Zeno's arguments contributed to the sense of disillusion with pre-socratic metaphysics which paved the way for the more sceptical tenor of the Sophists.

Parmenides was, by contrast with Heraclitus, sceptical about the possibility of movement or change of any kind. Clearly he must have disbelieved his senses. He takes one step further than Heraclitus by sourcing his doctrine, not on mere introspection, but on reason. In this he may be the first precursor for that kind of scepticism found for example in David Hume in which demonstrative proof is taken to be the only source of certain knowledge.

Bertrand Russell, in his History of Western Philosophy Russell46 locates the beginning of scepticism and of a decline in the vigour of Greek philosophy, with Protagoras and the sophists. Protagoras observed that "Man is the measure of all things ...", which is usually taken as a radical relativism, denying objective truth and hence as essentially sceptical (and, Russell suggests, based on the 'deceitfulness' of the senses).

The most explicitly sceptical of the sophists appears to have been Gorgias, who maintained that:

• nothing exists
• if anything did exist, we could not know it
• if anything could be knowm, we could not communicate that knowledge

and went on from there to devote himself to rhetoric.

More generally, in the sophists rhetoric becomes more highly valued than the search for truth or wisdom.

One of Socrates' best known statements is to the effect that he is wiser than others only by virtue of knowing his own ignorance. It is possibly this kind of generally sceptical observation which made Cicero attribute his own view that nothing could be known (except that almost nothing can be known) to Socrates.

Socrates does deploy to great effect, if Plato's Socratic dialogues are veridical, the method of refutation by reductio absurdum which is later systematised in the Pyrrhonean tropes. But the Socrates presented by Plato is by no means universally sceptical, he is devoted to demonstrating the truth of a broad ranging systematic philosophy.

Plato's scepticism is conspicuous in the most fundamental part of his philosophy, the theory of forms, which is justified and explicated in his simile of the cave and is based on scepticism about the senses. Plato's realm of forms is one of which we can obtain reliable knowledge, through reason, of intelligible objects, by contrast with the unreliable knowledge of the world of appearances which we obtain through our senses.

This is a specific area of scepticism, though fundamental in Plato's philosophy, not the kind of broad all encompassing scepticism found in the academic and pyrrhonean sceptics.

The term "academic" here refers to the academy of Plato which gradually adopted academic scepticism after the death of Plato. Pyrrhonean scepticism begins later (see below) but ran alongside (temporally) rather than superseding academic scepticism.

It is common, even today, casually to dismiss the sceptic on the grounds that he is inconsistent in claiming to know that no knowledge is possible. This argument is so simple that there can have been few sceptic who were not aware of it. It was certainly known (if not known certainly) early in the history of Greek scepticism.

A simple, if perhaps somewhat ad hoc escape from this charge is to admit one exception, claiming to know that nothing can be known except that nothing but this one proposition can be known. Apparently Cicero took this position and attributed it to Socrates, though this attribution is conspicuously contradicted by Plato (if his Socratic dialogues are to be taken as historically accurate).

Academic sceptics who made no exception are said to include Arcesilas and Carneades. I don't know how they deal with the allegation of inconsistency. One possibility is to express belief without claiming knowledge. "I believe, but do not know, that no knowledge is possible.". Better, perhaps, to avoid even a statement of belief and be content with an expression of doubt "I doubt that knowledge is possible".

The most extreme and systematic scepticism in the philosophy of the ancient Greeks was that of Pyrrho of Ellis and the sceptical tradition which followed him. Pyrrho added moral and logical scepticism to the scepticism with regard to the senses which had preceded him, and is said to have held that there could never be any rational ground for preferring one course of action over any other.

The most thorough and consistent sceptic reserves judgement on all matters, save perhaps that "appearances appear", and this attitude is echoed in those positivist philosophers who advocate that science should do no more than record the results of experiments. Because positivists often have this element of sympathy even for extreme scepticism I propose here to discuss such scepticism in ways which are perhaps better informed by positivist than pyrrhonean philosophy.

In the parlance of sceptics a dogmatist is anyone who has a definite belief. There is of course a risk for sceptics of slipping into dogmatic scepticism by asserting that nothing can be known (except perhaps the content of our sensory experience), and this is evident in some positivist philosophers.

It may be argued that we lack knowledge of the external world because our conclusions about it are derived from the evidence of our senses, which is unreliable, but more important, which, reliable or not, does not logically entail any conclusion about the external world. It is logically possible that our senses should yield information which is entirely disconnected with the condition of the world, that they do not, however reliably, is contingent. In this argument is implicit the presumption that to have knowledge of a proposition we must be posessed of evidence which logically entails the proposition under consideration.

This is an important kind of scepticism for positivism, and is prominent in the philsophy of David Hume. It can be described in foundationalist terms by observing that our knowledge of the external world is derived entirely from the data provided to us by our sense, but even the most simple judgements of perception go beyond what is given to us by our senses. Some kind of process

It seems odd to count metaphysicians a sceptics, but this is way Margaret Wiley does in [Wiley52], The point of interest to her is the combination of scepticism in these poets with religious faith. The scepticism was probably both with respect to the dogmatic religious controversies of the time and also in respect of any tendency for growing scientific knowledge to imping on the domain of personal faith.

Bayle's scepticism seems to have been fairly general though he did have a particular concern with dogmatic religious controversy. He believed human reason better adapted to discovering errors than for establishing positive truth. He though reason incapable of establishing the existence of god, and rather that his existence was repugnant to reason, thereby establishing faith as a greater accomplishment than it might otherwise have been. He considered morality independent of religious belief, as powerfully motivated by non-religious belief as it might be by religious beliefs, and more generally doubted the connection between belief and practice.

Four features enumerated by Kolakowski as characteristic of positivism: phenomenalism, nominalism, status of value judgements, unity of science.

Other features which may be present, such as empiricism, scepticism, semantic doctrines (verification, utility, pragmatics), methodology for science and philosophy, foundationalisms.

Scepticism has a long history.

The views of some late medieval philosophers may be said to have elements of positivism in them, and contributed towards the separation of scientific knowledge from metaphysics and a separation of secular from ecclesiastical matters.

According to Kolakowski, "the Enlightenment had a positivism all of its own".

Hume scores well on all of Kolakowski's key features and is therefore considered the first full blooded positivist.

Comte is the founding father of positivism, the first to deliberately formulate a positivist philosopher abd the person who gave the position its name.

My notes on the book by Leszek Kolakowski.