We should strive to achive the simplest sets of inductions that describes erey observed relations between the phenomena. This set inductions (also called theories) will be called descriptive theories. If the sets of inductions also enable us to manipulate phenomena preciasly<ref>Habermas, J. (1985). The Theory of Communicative Action, Volume 1: Reason and the Rationalization of Society (p. 465). Beacon Press.</ref> it will be called forcasting theories. The inductions are like equations that describe phenomena in more economical way<ref>Ernst, M. (1986). On the Economical Nature of Physical Inquiry. Popular Scientific Lectures (pp. 186–214). Open Court.</ref>.

==The Structure of Theories==