"The degree of life which appears in a thing depends upon the life of its component centers and their density. Following are fifteen structural features which Christopher Alexander has identified as appearing again and again in things which have life. 

Together, these fifteen properties identify the character of living systems. They are the principal ways in which centers can be strengthened by other centers. They are not independent, but rather rely on and reinforce each other. Things which are more whole, which exhibit more life, will have these fifteen properties to a strong degree. Conversely, the things in this world which are most lifeless will have these properties to the least degree." - TKWA

Read more and see excellent illustrations and photos of the 15 properties:

- The Fifteen Fundamental Properties of Wholeness