True to his empiricism, Locke tries to construct the idea of God — that is, an infinite being — from his finite experiences. Starting with the reflective knowledge of your own mind and your finite experience of human existence — duration, knowledge, power, wisdom, and all other positive qualities — Locke says in his Essay, “We enlarge every one of these with our idea of infinity; and so putting them together, make our complex idea of God.”

Two things should be noted. One, Locke differs greatly from the rationalists. Rationalists like Anselm and René Descartes use conceptual proofs in their attempts to prove God's existence. They define God as a supreme being whose very essence implies his existence. For Locke this would not do, since for Locke God is a complex idea extrapolated from an individual's own ideas of finitude. To begin to assert God's existence by using an idea of perfection is, as he states in Essay, “an ill way of establishing his truth and silencing atheists.” He reasons that (a) some people lack an idea of God altogether, and (b) among those who possess ideas of God, their ideas are at variance.

Cosmological Argument

In one respect, Locke is hardly different from several medieval philosophers. For instance, he is similar to Thomas Aquinas in the manner that he argues for the existence of God. Locke's argument is mainly “cosmological” and fits the definition of what he calls “demonstrative knowledge.”

Locke believed that you could prove the existence of God with the same degree of certainty that you can deduce conclusions in geometry.

That is, he believed that since you know that nature is a system of causes and powers, you must conclude that there is an original, supreme source of this system, namely, God.

On the one hand, nature could not have existed eternally; on the other hand, it could not have come from nothing, for then it would be uncaused. Therefore, it must have been brought into existence by a supremely intelligent being.

His conclusion combines premises found in Aquinas, especially his second “casual” argument and his fifth “design” argument, with rational intuitions found in Descartes. He used Descartes's intuitions that:

• Something cannot come from nothing.

• The cause must have all the perfections that it imparts to its effect.

From these considerations he deduces the existence of an eternal, powerful, and intelligent cause.

Morality

There are no innate moral principles “written on the heart,” Locke said. Since Locke rejected the notion of innate ideas, moral, political, and religious ideas must be regarded as arising from experiences. Since you have no direct sensations corresponding to good and evil, you must find other sensations from which these notions are derived.

As might be expected with an empiricist philosopher, Locke begins with the experiences of pleasure and pain. Simply put, you call “good” whatever tends to cause pleasure and “evil” anything that tends to produce pain. In this manner, he is not unlike Epicurus and Hobbes before him.

Locke, however, goes beyond the standards of the individual in assessing morality and turns to the standards of society. In fact, moral good and evil must be in conformity with or opposed to the law of the land. There are three kinds of laws:

• The divine law

• The civil law

• The law of opinion or reputation

Because the last two have their origin in human values, they will be of relative value, depending on the time and place being considered. The laws of one land will allow for practices that are prohibited elsewhere.

That said, Locke believed, perhaps naively, that conformity to God's law tends to advance the general good of humankind. Further, he argued, there is at least a core of agreement among civil law, divine law, and the law of opinion or reputation. All three would no doubt agree that stealing and killing are evil and that generosity and consideration for others are good. Locke claimed in Book II of the Essay that God's law may be discovered either through “the light of nature” or “the voice of revelation.”

Locke ventures on to shaky ground, however, when he displays his rationalist colors. He concludes in his Essay that “morality is capable of demonstration as well as mathematics.” Among his candidates for rationally demonstrable principles, he includes “Where there is no property there is no injustice.” He claims, amusingly, that this is as certain as any demonstration in Euclidean geometry. But, obviously, there are many injustices that don't involve property.

When he returns to his empiricist foundation, he seems to occupy sturdier ground. Though the moral codes of societies differ, he says, there is a high degree of uniformity among them. Why is this so? Locke's answer is that experience teaches which kinds of behavior are beneficial and which are not. Thus, the law of opinion or reputation carries its own wisdom, since it is based on the collective experience of citizens. Indeed, societies know well that killing, stealing, and other practices fail to advance the satisfaction of the community.