When the great thinkers of Greece laid down rules for valid reasoning, they had, it is true, the needs of politics specially in their minds. After the prisoners in Plato's cave of illusion should be unbound by true philosophy it was to the service of the State that they were to devote themselves, and their first triumph was to be the control of passion by reason in the sphere of government. Yet if Plato could visit us now, he would learn that while our glass-makers proceed by rigorous and confident processes to exact results, our statesmen, like the glass-makers of ancient Athens, still trust to empirical maxims and personal skill. Why is it, he would ask us, that valid reasoning has proved to be so much more difficult in politics than in the physical sciences?
Our first answer might be found in the character of the material with which political reasoning has to deal. The universe which presents itself to our reason is the same as that which presents itself to our feelings and impulses—an unending stream of sensations and memories, every one of which is different from every other, and before which, unless we can select and recognise and simplify, we must stand helpless and unable either to act or think. Man has therefore to create entities that shall be the material of his reasoning, just as he creates entities to be the objects of his emotions and the stimulus of his instinctive inferences.
Exact reasoning requires exact comparison, and in the desert or the forest there were few things which our ancestors could compare exactly. The heavenly bodies seem, indeed, to have been the first objects of consciously exact reasoning, because they were so distant that nothing could be known of them except position and movement, and their position and movement could be exactly compared from night to night.
In the same way the foundation of the terrestrial sciences came from two discoveries, first, that it was possible to abstract single qualities, such as position and movement, in all things however unlike, from the other qualities of those things and to compare them exactly; and secondly, that it was possible artificially to create actual uniformities for the purpose of comparison, to make, that is to say, out of unlike things, things so like that valid inferences could be drawn as to their behaviour under like circumstances. Geometry, for instance, came into the service of man when it was consciously realised that all units of land and water were exactly alike in so far as they were extended surfaces. Metallurgy, on the other hand, only became a science when men could actually take two pieces of copper ore, unlike in shape and appearance and chemical constitution, and extract from them two pieces of copper so nearly alike that they would give the same results when treated in the same way.
This second power over his material the student of politics can never possess. He can never create an artificial uniformity in man. He cannot, after twenty generations of education or breeding render even two human beings sufficiently like each other for him to prophesy with any approach to certainty that they will behave alike under like circumstances.
How far has he the first power? How far can he abstract from the facts of man's state qualities in respect of which men are sufficiently comparable to allow of valid political reasoning?
On April 5th, 1788, a year before the taking of the Bastille John Adams, then American Ambassador to England, and afterwards President of the United States, wrote to a friend describing the 'fermentation upon the subject of government' throughout Europe. 'Is Government a science or not?' he describes men as asking. 'Are there any principles on which it is founded? What are its ends? If indeed there is no rule, no standard, all must be accident and chance. If there is a standard, what is it?'[[25]]
Again and again in the history of political thought men have believed themselves to have found this 'standard,' this fact about man which should bear the same relation to politics which the fact that all things can be weighed bears to physics, and the fact that all things can be measured bears to geometry.
Some of the greatest thinkers of the past have looked for it in the final causes of man's existence. Every man differed, it is true, from every other man, but these differences all seemed related to a type of perfect manhood which, though few men approached, and none attained it, all were capable of conceiving. May not, asked Plato, this type be the pattern—the 'idea'—of man formed by God and laid up 'in a heavenly place'? If so, men would have attained to a valid science of politics when by careful reasoning and deep contemplation they had come to know that pattern. Henceforward all the fleeting and varying things of sense would be seen in their due relation to the eternal and immutable purposes of God.
Or the relation of man to God's purpose was thought of not as that between the pattern and the copy, but as that between the mind of a legislator as expressed in enacted law, and the individual instance to which the law is applied. We can, thought Locke, by reflecting on the moral facts of the world, learn God's law. That law confers on us certain rights which we can plead in the Court of God, and from which a valid political science can be deduced. We know our rights with the same certainty that we know his law.