The word "nature" has two major meanings - the essence and identity of a thing, and the entirety of all existing objects, at least those not created artificially by humans. In classical science, the behavior of an object and its "nature" in the first meaning are defined by some universal and unchanging "natural laws". The system of all such laws determines nature in the second meaning of its entirety. The concept of "natural laws" did not exist in antiquity - it is not found in Aristotle, Plato, or Archimedes. Leonardo da Vinci, Galileo and Kepler do not use it either. Some other Renaissance authors, however, began leaning towards this concept, in particular when they compared true knowledge about nature with the defin-itiveness of legal knowledge. From the need for such comparison, the humanist ABSTRACTS197 Coluccio Salutati arrived at the idea that an analog of human laws had to be found in nature.