Four assumptions are made in this theory. The logarithmic flow curve, specific viscosity against shear rate, has three linear segments which correspond to first Newtonian, power law, and second Newtonian regions of shear rate. The logarithmic plot of primary normal‐stress difference against shear rate also has three linear segments, in the same regions. Within any shear‐rate region the logarithm of a rheological property depends linearly on the logarithms of all parameters; these include volume fraction and molecular axial ratio. One long and one short characteristic time determine behavior at low and high shear rates, respectively. From these assumptions it is shown that the rheological properties are then so interrelated that many properties can be predicted if a few are known. Detailed theories for dilute solutions, given in a review by Brenner, confirm these relationships. New predictions for semidilute concentrations at high shear rates are derived from the theory of Doi and Edwards, which is also shown to represent Newtonian data at low shear rates from this laboratory better than the earlier equation of Brodnyan. At high shear rates not only the viscosity but also the normal stress become constant; this requires the relative importance of elasticity compared with viscosity to go through a maximum in the power law region.