The edifice of modern physics is a great intellectual achievement of mankind. Based on the work of many scientists, from Bacon and Newton to Einstein and Feynman. It consists of a relatively small number of laws that appear to govern everything that occurs. What this means is that almost no one expects that observations will be made that are inconsistent with these basic laws. That does not mean, however, that the laws can predict everything. Actually, the basic laws predict nothing. It is always the case that they are useful only in conjunction with auxiliary hypotheses and models tailored to make the resulting combination of laws and hypotheses adequate and pertinent to particular observations.

In most cases in the physical world and a few cases in the biological world, the auxiliary hypothesis of linearity is sufficient. In a few cases in the physical world and almost all cases in the biological world the auxiliary hypothesis of nonlinearity is required. In few cases in the physical world and no cases in the biological world, the precise structure of the nonlinear model has been identified.