From the introduction of A New Theory of Urban Design by Christopher Alexander, et al:

When we say that something grows as a whole, we mean that its own wholeness is the birthplace, the origin, and the continuous creator of its ongoing growth. That its new growth emerges from the specific, peculiar structural nature of its past. That it is an autonomous whole, whose internal laws, and whose emergence, govern its continuation, govern what emerges next.

We feel this quality very strongly, in the towns which we experience as organic. To some degree we may know it as a fact about their history. To some degree we can simply feel it in the present structure, as a residue.

This kind of growing wholeness is not merely something that existed in old towns. It exists, always, in all growing organisms (which is why we feel that old towns are somehow organic … simply because they share, with organisms, this self-determined, inward-governed growing wholeness). And it exists, also, in all great works of art. It exists in a good painting, during the time of its creation. It exists in a poem.

In each case, we are aware that the future growth of the thing is created, from the present, by an impulse towards wholeness. Somehow, this impulse […] is allowed to govern the next steps in the creation, the expansion, the formation of details … the formation of the largest and the smallest wholes.

This feature exists, also, in a dream, whose evolution is again governed by the history of where it has been so far. And it exists in a children’s bedtime story, made up as we go along. Each sentence, coupled with the child’s delight, tells us what fantastic thing will happen next, inspires us to fill out the fantasy, to bring it back upon itself, again to make it whole.

If the book continues like this, it is a brilliant one. Next, he goes on to talk about fundamental and essential features of growing wholes. “First, the whole grows piecemeal, bit by bit. Second, the whole is unpredictable. When it starts coming into being, it is not year clear how it will continue, or where it will end, because only the interaction of the growth, with the whole’s own laws, can suggest its continuation and its end.” And so on. You can read more at Amazon.com.