suggest. Rather, he means that there are certain constraints that determine what it is to follow a valid line of reasoning, constraints that we are required to follow, like it or not. To be sure, we may not in actual fact always observe those constraints in our thinking: people often make mistakes in argument and reason badly. But there is nonetheless an authentic way, a way we ought to go, a way we can on reflection recognize as valid, independently of where we might like to go. To borrow another metaphor, used many centuries later by the German logician Gottlob Frege, the laws of logic could be said to be like boundary stones which our thought ‘can overflow, but not dislodge’.2
The Greek word for ‘argument’ is logos, from which we get the English word ‘logic’. A good argument is not just a series of thoughts, but a logical sequence, where the final step or conclusion follows logically from what has gone before. An argument is said to be valid if, once you grant the truth of the premisses (the assumptions or starting-points of the argument), the conclusion must follow. Thus, in a time-honoured example, if your two premises are that (1) all humans are mortal, and (2) that Socrates is human, then it follows that (3) Socrates is mortal. This very strong form of argument is called a deductive argument, meaning that the conclusion can be logically deduced from the premises. And this in turn means that anyone who accepts the premisses has to accept the conclusion on pain of contradicting themselves.
To assess a deductive argument, you have to do two things. First you have to assess whether it is valid: does the conclusion follow as a matter of logical inevitability from the premisses? This is a purely formal matter, and in many cases it can be quite straightforward. In the above example about Socrates being mortal, the form of the argument is, ‘if all As are B, and x is A, then it follows inevitably that x is B’. This pattern or reasoning is universally valid whether we are talking about Socrates and mortality, or any other objects or properties whatever; so if all swans are white, and Fluffy is a swan, it follows that Fluffy is white. Notice, however, that although this latter argument is perfectly valid, just as in the Socrates case, its starting point is questionable. Few if any of us would concede the first premiss (that all swans are white), since we know that there have been cases of black swans. So validity in argument is not the only thing that matters. We want our arguments to be valid, but we also want the premisses to be true. And only then will we say that the argument is not just valid but acceptable or sound: the premises are true, and the conclusion logically follows. Often in philosophy some of the most interesting questions arise not about the validity of an argument, but about whether the premisses are true.
So although formal logical skills are important in philosophy, they are not the whole story. Indeed, philosophical arguments, as they occur in the great canonical texts, are very seldom set out in simple deductive patterns like that in the Socrates example just mentioned. The arguments are generally more complex, and they have to be extracted from the flow of the writing, with the implicit premises teased out and examined, and the possible vagueness and ambiguities scrutinized. And in deciding whether a given premiss should be accepted in the first place, one often has to reflect carefully on just exactly what is being claimed, and what implications it has for the rest of one’s worldview.
An Example from Berkeley
To consider just one example of how one might set about expounding and criticizing a philosophical argument, let us take a passage from a well-known text by the idealist philosopher George Berkeley – his Principles of Human Knowledge, first published in 1710. Berkeley’s aim, as is explained in the introduction to the full extract (to be found in Part II, Section 6), was to argue that nothing exists independently of a mind. Here is part of what he says:
It is indeed an opinion strangely prevailing amongst men that houses, mountains, rivers, and in a word all sensible objects, have an existence natural or real, distinct from their being perceived by the understanding. But with how great an assurance and acquiescence soever this principle may be entertained in the world, yet whoever shall find in his heart to call it in question, may, if I mistake not, perceive it to involve a manifest contradiction. For what are the forementioned objects but the things we perceive by sense? and what do we perceive besides our own ideas or sensations? and is it not plainly repugnant that any one of these or any combination of them should exist unperceived?
The first task is to get behind the rather elaborate phrasing of Berkeley’s eighteenth-century English and extract the basic train of thought, which is actually quite straightforward. In the first sentence, Berkeley talks about ‘houses, mountains, rivers’, in short, the ordinary objects around us. And he refers to the widely held or prevailing opinion that they exist independently of their being perceived (‘they have an existence natural or real, distinct from their being perceived’). Now think about this: do you share this prevailing opinion? Do you think houses and mountains have ‘real existence’, distinct from their being perceived? The obvious answer is that yes, we all do share this view: we think the houses and rivers are still there, twenty-four hours a day, as it were, whether or not we are there to look at them or think about them. Indeed, if all human beings and other sentient creatures were suddenly to vanish from the earth, the mountains would still be there, would they not?
But what is Berkeley saying about this ‘prevailing’ opinion, this ordinary common-sense view of the real independent existence of mountains, rivers and houses? He says it is a strangely prevailing opinion: widespread though it may be, it is odd (Berkeley seems to be saying) that people accept it. And he goes on to say that once we start to question it (‘whoever shall find in his heart to call it in question’), we find it is obviously absurd (it involves a ‘manifest contradiction’). Why? Because, says Berkeley, all these aforementioned objects are things we ‘perceive by sense’ (that is, by seeing, hearing, touching, and so on). And, he goes on, ‘what do we perceive besides our own ideas or sensations?’ He puts it as a rhetorical question, but he means to state it plainly and outright: we only perceive our own ideas or sensations.
By the time we have reached this point, we are in a position to see where Berkeley is going. Obviously, ideas and sensations depend on the mind of the perceiver. Ideas and sensations can’t exist independently, outside of a mind. So if (as Berkeley is asking us to accept) we only perceive our own ideas and sensations, then what we perceive cannot exist outside a mind. So the ‘sensible objects’ – the mountains, houses, rivers, etc., that people think of as existing independently ‘out there’ – cannot after all exist except as ideas or sensations in the mind.
I hope this gives some idea of how you might set about the first task of a philosophy essay – the task of exegesis, of unpacking an argument, teasing out the train of thought, breaking it down into its stages. A lot of philosophical writing involves this kind of analysis, which in its original Greek sense means untying, or unravelling. Unpacking a whole text in this way would take a very long time, and (as will be seen if you turn to the whole extract in Part II, section 6) Berkeley has a lot more to say than what is contained in the paragraph above. But part of your job in a philosophy essay is to be selective – to work out which particular passages to concentrate on as containing the key arguments, or as representing the crucial elements of a given position.
What about the other component of a good philosophy essay, namely criticism? Here you would need to stand back from what Berkeley is saying and ask which are the crucial premisses on which his argument depends, and whether they are plausible. Probably the most controversial element in the train of thought unpacked above is Berkeley’s claim that we only perceive our own ideas or sensations. Is this true? When you look at a mountain or a house or a river, what are you perceiving? Perhaps the obvious answer is – the mountain, the house, the river. We do not normally say that we see ideas of houses, or look at sensations of rivers; we say that we see houses and look at rivers. So is Berkeley forcing a card on us – softening us up to accept his immaterialist view of reality? It’s true of course that we couldn’t perceive any of the objects around us unless we were equipped with sense organs that respond to the relevant stimuli.
