The secret Strength of things/ Which governs thought, and to the infinite dome/ Of Heaven is as a law, Inhabits thee! – Shelley, “Mont Blanc”

Because of Plato’s use of the term to describe his view of the most basic realities, this term has become one of the most fundamental philosophical concepts. In Greek, the term is eidos, which meant shape, outline, or image. (It forms the root of the English word ‘idea’, but this usage to refer to an object of thought did not arise until the 17th century.)

How did the simple word for image or outline become the most important philosophical concept in history?

The beginning of the intellectual life is the recognition that things have similarities and that the key to their actions lies in these shared features. Two triangles share a common outline or shape, and most of their significant properties will arise from this shared form, rather than the things that distinguish them such as their position, what they are made of, and the unique defects that distinguish each one. This is the beginning of the recognition that there is more to the world than meets the eye. They key to a turtle or a tree or a triangle does not lie in what we see on the surface of each particular instance, but in the hidden source of the similarities we grasp between them. When we see disparate things, with no causal relationship that we can see, having similar properties and acting in similar ways, it becomes clear that these things must be connected on some level that goes beyond their mere appearances. There is a secret source of the similarity in the particular objects that populate our world. The order of the world that we perceive in the apprehended similarities of the objects we encounter has a source, a single ordered source, of which the objects we see and their similarities are copies. The idea of form gave rise to the view that the universe is a kosmos, an ordered whole.

Equally important is the fact that we are capable of grasping these similarities, that, in fact, our mind leaps to uncover them and feels gratification and pleasure at their recognition. Not only is the most important feature of reality the secret source of its order, revealed by our grasp of similarities, but also our most important feature: the unity of our faculties with the hidden principle of the kosmos. There is something that draws the flux of appearances to order, and that something draws us as well. We can feel our connection with the secret source of things in our drive to apprehend form and our perception of form as beauty.

In the concept of form lies the source of the dual beliefs that the most important part of reality are the abstract essences that things share and that the most important part of us is the faculty that grasps them. Of course, in modern times we like to pierce the veil that hides the secret source of things and find the physical laws that explain the order we find in things in terms of their composition and history. We like to find explanations of the working of our minds within the laws that govern the more basic forms of our brains. But the source of the similarities that lie at the heart of even these basic scientific laws remains hidden, and our mind still yearns to discover it.