Humans are rational animals, that is, we are creatures that can apply a mental faculty to the understanding of events and actions. This has its roots in the very biological need to perceive the necessary consequences of certain actions: IF I put my hand in the fire, THEN I will be burnt. IF I go to the waterhole at dusk, THEN I might be able to kill one of the animals drinking there, AND I might gain some food. This faculty, this capacity to reason, is indeed a marvellous attribute.
In the paragraph above, I capitalised certain words: IF, THEN, AND. Computer programmers might recognise them as logical commands – in other words, they are commands which a computer can execute. The computer knows what to do when a program includes such terms – that is how it has been set up and programmed – and the computer will happily pursue such commands for as long as the person doing the programming wishes it to. When I was younger I learnt how to program computers using the language BASIC, which included terms like these. One of the most important elements in the programming was the IF…THEN command. This allowed the computer to make ‘choices’ according to certain established criteria. Perhaps the program wanted to ask the observer to press a certain key to indicate ‘yes’ and another key to indicate ‘no’ as an answer to the question that the computer was asking. The programmer could then write IF (keypress = ‘Y’) THEN do one thing, but IF (keypress = ‘N’) THEN do another thing. Of course, my language there was a little inaccurate – the computer is not making a real choice – it is simply following the predetermined path laid down by the programmer. The programmer wanted to give the user of a program a choice at this point, and has instructed the computer to react to that choice in the appropriate way.
What I would like to bring out from this example is the way that reason follows a set pattern – we even have the phrase ‘a chain of reasoning’ to talk about such patterns – and a computer program is a very clear example of the pattern in which reasoning functions. This pattern which reason follows has its own name: logic, and reason and logic are essentially linked. Logic is the study of these patterns or chains of reasoning, and the usefulness of logic lies in the way that it can show how some chains work (i.e. are ‘valid’) and some chains do not. To go back to the example of a computer program, the line of programming could read: IF (keypress = ‘Y’) THEN do such and such ELSE IF (keypress = ‘Y’) THEN do some other thing. When the computer follows the program and gets to this point then it will become stuck and ‘crash’. This is because the command has told it to do two different things at the same time. If the user presses the Y key then both sides of the argument are satisfied – and the computer will have to do both!
Another way of thinking about this same point is to talk about consistency. In the example of bad programming above, the source of the difficulty was that ‘Y’ was given as the ‘keypress’ in both cases. One or other should have been ‘N’ – or, even, ‘any other keypress’. This line of programming was therefore inconsistent – it was asking the computer to do two different things if the keypress was ‘Y’. Let’s go back to the waterhole – imagine a brain set up like a computer, with instruction sets that stated: IF it rained yesterday THEN go to waterhole today at dusk, but also, IF it rained yesterday, gather fruit from trees. In this situation, the person concerned is given two incompatible instructions – gather fruit or go to the waterhole? Chances are the poor individual will just stay where they are, unable to reconcile the contradiction, until some other impulse takes over and the situation changes.
To put this in the language of logic, the program at this point is invalid, and in computer programming to call a program ‘invalid’ is to say that there is something wrong with it, that it has a ‘bug’. Although the situation gets much more complicated with today’s software, in essence this is what happens when any computer crashes – it is trying to carry out commands that don’t ‘make sense’. The millennium bug caused some concern a little while ago – this was, in principle, just such an example of invalid programming. Computers were set up to recognise dates by only the last two numbers in the year – so 1999 was simply ‘99’, for example. This was because the computers were programmed in the 1960’s and 1970’s, and the assumption was made (either consciously or unconsciously) that they would be changed before the year 2000 came along. So, in the programming, a certain assumption was built in – all years would be 19xx, where the xx was the date supplied by the user. The millennium bug happened because this assumption became untrue from the year 2000 onwards. Consequences followed from this mistake, which at some point were believed to be on the scale of a minor apocalypse, although in practice we were spared such a judgement.
So logic is really a way of working out if something makes sense, either in terms of an argument being able to follow on properly (like a computer program) or in terms of one thing being consistent with another. Consider the following, which is something of a classic:
1. All men are mortal
2. Socrates is a man
3. Socrates is mortal.
This is an argument: that is, it is the assertion of one item (3) as a consequence of the assertion of two other items (1 & 2). It is saying: because 1 & 2, therefore 3. In some ways it is a similar argument to a computer program which uses IF…THEN language. IF 1 & 2, THEN 3. As it happens, this argument is a valid argument, and it is worth unpicking why it is valid, and precisely what it means to say that the argument is valid.
The first item, 1, defines an attribute of men, stating that they are mortal. The second item, 2, states that Socrates belongs to the class of men. The third item draws the logical consequence of these two items: Socrates is a man and therefore shares the attribute that all men share – mortality. As such, Socrates is mortal. To say that this argument is valid is to say that the conclusion follows from the premises, that it makes sense. If it were a computer program you would say that it didn’t have any bugs in it. In this argument, the conclusion necessarily follows from the premises (philosophers say that the conclusion can be deduced from the premises) – in other words it has to be the case that, IF 1 & 2 are true, THEN 3 also has to be true. There are no situations in which 1 & 2 are true, and 3 is not. This is what is meant by a valid argument: that the logic is sound, there are no ‘bugs’.
However, although interesting, this is not ultimately very exciting. This is because logic and valid argument tell us nothing about truth, or how things are in the world. Consider the following adaptation of the above argument:
1. All men are born with two heads
2. Socrates is a man
3. Socrates was born with two heads.
In terms of the logic of this argument, there is nothing to choose between this argument and the original; they are both equally valid. Yet the first argument says something true, the second says something that is not true. This is because logic is not concerned with truth or falsehood, but only with consistency and the validity of arguments. The difference between these two arguments – one says that all men are mortal, the other says that all men are born with two heads – is not something that logic can be employed to decide between. Whether men are born with two heads or not is not a question about the validity of a particular argument but about what is the case – is it true that all men are born with two heads? In the normal course of events, this is a question that would be answered by looking at the evidence of our senses – have we tended to see men always born with two heads? Are one-headed men carrying wounds where one head was taken away at birth?
In order to establish the truth in this situation, then, we would need to employ a different tool of our understanding. This is a crucial point to bear in mind: logic is a tool, it is not the source of all enlightenment. Think of the tools in a tool-box; there is a hammer, a chisel, a hacksaw, a spanner. It would not be appropriate to use a spanner to separate a plank of wood into two halves – there you should use a saw. In a similar way, although logic is a wonderful and essential part of human life, it is not the only tool that we have when we are reflecting upon the true nature of our world – it must be used in the correct place, in the correct way, and not elsewhere.
So can we use logic to determine which account is the best, between Dawkins, Gould and all the others? Well, it will certainly assist (it might point out some self-contradictions in an argument), but on its own it is not much help. That is for the simple reason that any position you like can be made logically coherent, if a person is prepared to take the consequences. As pointed out above, something can be perfectly logically valid and still be untrue (Socrates has two heads). Consider: although I have never met someone who believes that the earth is flat, I am assured that there is a ‘flat-earth society’, whose members believe that the earth is not a sphere in orbit around the sun, but is instead a flat disc, with edges, and that it is possible to fall off the edge. You might think that it is impossible to make such a belief consistent, that it is impossible to be a logically consistent believer in a flat earth. Yet what arguments would be persuasive? Pictures of the earth as a globe could be fabricated; stories of travel around the world might be fables to lure the unwary; various physical tests could be written off as optical illusions. Even if it were possible to take such a believer out into space so that they could see for themselves that the earth is a globe – “Look! See! It IS round!!” – that would not necessarily succeed. The believer could say “I have been drugged; you have set up a theme park providing this remarkable illusion. My eyes see a globe, but I do not believe my eyes…” And so on.
You can lead the horse to water but you cannot make it drink. So our analysis must shift to the second of our standard criteria: questions of evidence. Even if we cannot reach a logically conclusive argument, we could at least gather together as much relevant evidence as possible and then let people make their own conclusions – and surely, there aren’t many people prepared to place logical consistency ahead of the straightforward evidence of their senses?