Proponents of the linear model and the neoclassical model have sometimes
been drawn into pointless arguments about which model is worse. Proponentsof the linear growth models point out that the neoclassical model fails to capture fact 4. Proponents of the neoclassical model observe that the linear
model cannot capture fact 2. This dispute is partly an outgrowth of the
convergence controversy. Both sides specify that output takes the form Y =
K'-PLP and then argue about whether P is bigger than zero (as the proponents
of the neoclassical model claim) or close to zero (as some versions of the linear
growth model suggest).
This is not a very useful debate. There are circumstances in which each
model can be a useful expositional device for highlighting different aspects of
the growth process, but presumably the agenda for the profession ought to be
to capture both facts 2 and 4 and pick up fact 5 to boot.