PHIL 41150: Political Philosophy
Dr. Robert Lane
Lecture Notes: Friday January 24, 2003

[6.] What a Ruler Must Know: The Form of the Good (Republic VI & VII).


As Socrates stated earlier, philosopher-kings must have knowledge of the Forms, especially Forms of such things as Beauty, Justice and Goodness ("the Good"). But there is an order of priority here: the Form of Goodness is somehow prior to those other forms: "none will know the just and the beautiful satisfactorily until he knows the good." (506a, p.123).


But there's a problem: such knowledge is extraordinarily hard to come by; in fact, Socrates himself claims not to have knowledge of the Good. (506c, p.124) Although Socrates does not himself know the Form of the Good (he can't explain what goodness is in itself, i.e., can't explain what it is in general for something to be good), he tries to elucidate it with three analogies: the analogy of the sun, the analogy of the divided line, and the analogy of the cave.


[6.1.] The Analogy of the Sun. The Form of the Good (to agathon) is analogous to the sun in at least two ways:


1. It renders other Forms intelligible.


...understand that I meant the sun when I spoke of the offspring of the good, begotten by it in a certain resemblance to itself--that is to say, bearing the same relation in the visible world to sight and to the visible, which the good bears in the intelligible world to mind and the knowable. (508b-c, p.125)


Just as the eye cannot perceive physical objects without a third thing (sunlight), so the mind cannot come to understand any of the specific Forms without a third thing (the Form of the Good).


It's the Form of the Good that makes all other forms intelligible. To truly understand what an table is, for example, it's necessary to understand what a good table is. A good table will have a flat surface and some number of legs and be capable of supporting other objects -- if you don't understand this, then you don't really understand what it is to be a table. In this way, the Form of Good makes the Form of Table intelligible. On Plato's view, all other Forms (including those of Beauty and Justice) are "illuminated" by the Form of Good in the same way.


2. It gives being to other Forms -- without the Form of the Good, there would be no other Forms.


...the sun supplies the visible things, not only the faculty of being seen, but also their generation, growth, and nutriment, though it is not itself the same as generation. ... like manner, the knowable not only derives from the good the gift of being known, but is further endowed by it with being and essence... (509b, p.126)


For a thing to be wholly and genuinely an x, then it must be a good x. For example, for a given object to be a table, it has to be a good table, at least to some degree. If a given object deviates too much from this ideal, it no longer deserves to be called a table. In other words, a sufficiently bad table is not really a table at all. Plato means something like this when he says that no Form (including the Form of Table) would be possible without the Form of Goodness.





[6.2.] The Analogy of the Divided Line.


Socrates asks us to imagine a line divided first into two unequal sections; the first represents the visible world and the second represents the intelligible world. Then imagine that each of those sections is divided into unequal sections proportionally identical to the first division.


the visible world:

"the world of things seen"


the intelligible world:

"the world of things thought"





images, such as shadows and reflections

objects, such as animals and plants, all manufactured objects, etc. things which the images in section A resemble

lower forms: forms of square, triangle, bed, table[i]; forms which the objects in section B resemble

higher forms: forms of beauty, justice, piety, courage, and (most importantly) goodness (to agathon)








[i] Plato himself discusses the Forms of Table and Bed at Republic 596b.

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