Aristotle's major work was nothing much--just gathering all the learning of the past and present, in the fields of science, philosophy, rhetoric, law, and literature, and organizing this knowledge into meaningful patterns which would be available to posterity. And we thought Plato was broad.

The result was philosophy developed on the largest possible scale. Aristotle's career established the great divisions of philosophy which are still accepted today, and he made enduring contributions in each of them. Let's look at these contributions, each in turn.

If we are going to organize all learning into one system, we will need a strategy. And so Aristotle's first contribution to philosophy and Western thought was to state the laws of logic as we know them today. He studied the structure of rational thought, seeking to define those essential principles which sustain all reasoned inquiry. And he succeeded.

We all employ three basic axioms whenever we think in ordered ways. First, we use what Aristotle called the law of identity: A is A, and it must remain so. In other words, we begin by identifying the reality we are seeking to understand. We name it, quantify it, qualify it. We first want to know what it is, and how it relates to the rest of reality.

Then we move to the second axiom of reason: the law of contradiction: A is B, or it is not B, but it cannot be both. Whenever we identify something, we also identify what it is not. And it cannot be both, or reason breaks down. The page on which you are reading these words is either visible or it is not. If we think it is both, we cannot think about it at all.

Now we're ready for the last axiom of logic: the law of the excluded middle: A is B or it is not B, but it cannot be both at the same time. A statement must be either true or false within a given logical context. We must choose.

These laws of logic have sustained rational inquiry from Aristotle to today. This effect has been both very good and very bad, for reasons we'll soon investigate.

The logical approach Aristotle brought to the work of philosophy was a distinct departure from Plato's dialogues on scattered subjects. But his greatest break with his master came not in strategy but in substance, literally.

Remember that Plato was convinced by Pythagoras that there is a world of Forms or Ideas, distinct from this physical world, and that this world is but an imperfect shadow of that which is real. This ontology was the foundation for Plato's approach to the soul, the physical universe, aesthetics, and the future.

Aristotle rejects this essential premise. Completely. He is certain that the Form, such as it is, is to be found in the material world itself. Rather than being a shadow of the real, the physical universe is the real. Why did Aristotle come to this monumental shift of worldviews? And why does it matter?

Aristotle begins in his usual logical way. Rational beings must know objective truths, or they are not rational. However, the Forms cannot be known objectively--they are the product of a speculative philosophical system, not empirical experience. And so the primary realities of life must be the individual things we perceive. As a result, the Forms (such as they are) must be contained in the objects themselves.

In this view, individual concrete entities are real and scientifically knowable. Aristotle calls these entities the "substance," the thing which actually exists. He takes Plato's Forms to describe the unchanging essence which gives the thing its definition and purpose. As a result, things can change in quantity, quality, and position, but they cannot change in themselves because of their form.

And so Aristotle's ontology incorporates Plato's insistence on objective truth and values, as it was learned from Socrates. He explains how the world can change (cf. Heraclitus) while affirming unchanging values and timeless truths (cf. Parmenides). And he makes it possible for philosophy to be relevant to the observable world of real life experience.

One example of this relevance is Aristotle's fascination with biology. He was the first to construct a system for naming, categorizing, and relating all living forms. Another example is his view of the universe. He saw the observable universe as eternal and all-embracing, with nothing (such as a world of Forms) outside it, and theorized that it is hierarchically ordered and subject to causation in every respect. His understanding of physics was formative until well after the time of Copernicus--for centuries, the heavenly bodies revolved around the earth in perfectly elliptical, rational orbits. Or so the world thought. Such theories and many others were motivated by Aristotle's shift from the unseen Forms to the observable Substance of life.

How does this new perspective change things? In every way. If Aristotle is right, there is no "spiritual" realm to be separated from the "secular." God is not distant from this material universe. Spirituality is best developed by studying the empirical things which surround us. Ministry happens by reaching the world we can see, not by escaping to the world we cannot.

In coming Fridays we'll watch this philosophical shift as it works itself out in monumental ways across Western culture.

Some of the most intellectual facts have the most mundane explanations. For instance, most Christians do not know that the letters of Paul are arranged as they are for this deeply spiritual reason: they go from longest to shortest. Many people do not know that "Bible" comes from Byblos, the town where ancient paper was harvested and processed, so that the Holy Bible is simply the Holy Book. And many theologians and other Christians use the word "metaphysics" without ever knowing its deeply intellectual etymology--it is so named simply because Aristotle's writings on this subject were placed after ("meta") his writings on physics in his collected works. Philosophical trivia is such fun, isn't it?

When we reach Aristotelian metaphysics, we come to the most significant single subject in his thought relative to Christian faith. Remember that Aristotle believed the physical universe acts according to predictable laws of cause and effect. All substances are in constant motion. So, he asked himself, where did all this motion begin?

It seemed reasonable to Aristotle to suggest that motion requires a mover. All observable experience suggests that this is so. And so an Unmoved Mover must be the first cause of all other motion. This Mover would be purely immaterial in nature, on the order of Mind, since all material things require something else to begin their motion. Unlike Plato's Forms, it can cause physical reaction by direct involvement with the material universe, since the Form is in the Substance.

And so Aristotle believed that a Mind exists, self-sufficient and containing all knowledge and motion within itself. This Unmoved Mover would be impersonal, with no capacity for individual relationship with us. We can accept the existence of this God, but we cannot know him (or it).

When we apply Aristotle's laws of logic to his theology, we soon see how incompatible his metaphysics are with Christian faith. God cannot be three and one, for this is a contradiction; Jesus cannot be fully God and man, for the same reason. If laws of logic prevail, the Bible cannot be fully inspired and yet the product of human personality; God cannot be sovereign over the future while allowing us free will. But these denials of Christian belief are no problem for Aristotle, for he holds none of these beliefs.

When a theologian uses non-contradiction as the test for all truth, know that Aristotle is pleased. But God may not be.