In common usage, people sometimes tend to use the words rational and logical somewhat interchangeably. The purpose of this post is to distinguish between these.
Logic is the set of rules that allows me to evaluate an arguement independent of its content, purely from its structure. Just as I use grammar to parse a sentence and determine the relationships between the words in the sentence, I use logic to parse an arguement and determine the relationships between the statements in the arguement. Just as a grammatical sentence may be meaningless (Colorless green ideas sleep furiously), a logical arguement may be meaningless or irrelevant. However, the analogy with grammar only goes so far. There are many different grammars and all of them are equally valid within the context of their application – a given language. Any consistently applied way of meaningfully combining words in a sentence forms a grammar. Grammar is a matter of convention. The same is not true of logic. The word itself has no plural. This is a striking fact. Think about it. It indicates that man cannot even conceive of a plural for logic. There can be no such thing as my logic vs your logic. Logic is the structure of coherant thought. It is a part of the mental apparatus that man is born with. It is implicit in the capacity to think. By implicit, I mean that I cannot choose to think illogically (though I may make mistakes). To identify mistakes in thinking, the implicit rules of logic need to be made explicit by identifying them. This is a science. Like all sciences, the science of logic also presupposes several things. In particular, it presupposes man’s ability to use logic (implicitly). Whether the word logic refers to the implicit set of rules or to the science which deals with identifying them depends on context. In this post, I am going to use the word logic to refer to the implicit set of rules.
Reason is the faculty of understanding and integrating sensory material into knowledge. Reason does not work automatically. To reason, man has to consciously choose to think and to direct his thoughts to achieve understanding. By directing thoughts, I mean preventing thoughts from wandering by staying focussed. Reasoning involves the use of logic. It also involves several other techniques. “Reason employs methods. Reason can use sense-perception, integration, differentiation, reduction, induction, deduction, philosophical detection, and so forth in any combination as a chosen method in solving a particular problem.” [Burgess Laughlin in a comment on an old post] Deduction obviously uses logic. I believe induction does too but the science on inductive logic is nowhere as well developed as it is on deductive logic. Sense-perception, integration and differentiation don’t use logic (Note: integration and differentiation refer to grasping the similarities and differences between various things). Reason then is not simply the faculty of using logic.
“Rationality is man’s basic virtue, the source of all his other virtues… The virtue of rationality means the recognition and acceptance of reason as one’s only source of knowledge, one’s only judge of values and one’s only guide to action.” [Ayn Rand, in The Virtue of Selfishness]
In the discussion that motivated this post, a colleague argued that if the use of reason does not guarantee correct decisions, it cannot be one’s only guide to action. A gut feeling or intuition might sometimes be a better guide to action. There are two separate issues here – the fact that the use of reason cannot guarantee correct decisions and the claim that intuition can be an alternative guide to action.
Consider intuition first. Intuition is an involuntary automatic evaluation of the available choices. There is no conscious awareness of the reasons for the evaluation. Intuition is a learnt response from previous experience. As such intuition is extremely helpful in any decision making process. However, the fact remains that in every voluntary decision – the sort of decision where there is enough time to reason – intuition is only one of the inputs to the use of reason. As long as I make a decision consciously and deliberately, reason remains the only guide to action. The only alternative is to evade the responsibility of a choice. Relying upon intuition is not irrational in itself. I might decide that I do not have sufficient knowledge to reach a decision and choose to rely upon intuition instead. As long as I identify the lack of knowledge, my decision is fully rational. Identifying the lack of knowledge (and hopefully doing something about it) will actually allow me to learn from the new experience and improve my intuitions for future use. Blindly relying on intuition – by default instead of by choice – will actually weaken my intuition in the long run. Intuition is one of the most valuable tools for decision making but it needs to be carefully cultivated by the use of reason for it to be good or useful.
It is important to stress that rationality (in the context of making a decision) involves the use of all my knowledge to the best of my ability. In particular, this includes knowledge of the time available, the relevance of prior experience and any known gaps in knowledge. It is this last aspect of rationality – the use of known gaps in knowledge – that is the motivation for the field of probability. Probability is about quantifying uncertainty by making use of all known information and postulating equal likelihood where no information is available. The consistent use of the equal likelihood postulate is at the heart of probability theory and it is what gives probability its precise mathematical characteristics. In modeling an outcome for an uncertain event, I start with a uniform distribution (every outcome is equally likely) and use available information to transform it into a more appropriate distribution. The parameters of the transformation represent a quantitative use of known information. The shape of the final distribution represent a qualitative use of the known information.
With this brief treatment of probability, I can now address the obvious fact that the use of reason cannot guarantee correct decisions. Consider an example. I have historical data for the exchange rate between a pair of currencies. I also have market quoted prices for various financial instruments involving the currency pair. To model the exchange rate at some future time with a probability distribution, I can use the historical data to establish the shape of the distribution and the market quoted prices to obtain the parameters of the distribution. If I had more information (say a model for other parameters that affect the exchange rate), I could incorporate that too. A decision based on such a model would be a rational decision. On the other hand, I could say that since the model does not guarantee success, I will simply use a uniform distribution (Ouch!! That is not even possible since the range for the exchange rate is unbounded. Let me simply restrict the range to an intuitive upper bound) with the arguement that the uniform distribution might actually turn out to be better. Yes, it might turn out to be better, but the arguement that it should be used is still invalid (Consequentialism is invalid and I am not going to argue this). Not all decisions can be formulated with precise mathematics like this, but the principle is the same. It is always better to use all my knowledge to the best of my ability.
Another aspect of the original discussion remains unaddressed – the claim that rationality is subjective. Since this post has already got long enough, I will just stress here that there is a difference between context-dependent and subjective.