  We investigate the dynamics of growth models in terms of dynamical system
theory. We analyse some forms of knowledge and its influence on economic
growth. We assume that the rate of change of knowledge depends on both the rate
of change of physical and human capital. First, we study model with constant
savings. The model with optimised behaviour of households is also considered.
We show that the model where the rate of change of knowledge depends only on
the rate of change of physical capital can be reduced to the form of the
two-dimensional autonomous dynamical system. All possible evolutional paths and
the stability of solutions in the phase space are discussed in details. We
obtain that the rate of growth of capital, consumption and output are greater
in the case of capital dependent rate of change of knowledge.
