But this is not all we know about human capital. This same force, admittedly
unobservable, has also been used to account for a vast number of
phenomena involving the way people allocate their time, the way individuals'
earnings evolve over their lifetimes, aspects of the formation, maintenance and
dissolution of relationships within families, firms and other organizations, and
so on. The idea of human capital may have seemed ethereal when it was first
introduced - at least, it did to me - but after two decades of research applications
of human capital theory we have learned to 'see' it in a wide variety of
phenomena, just as meteorology has taught us to 'see' the advent of a warm
front in a bank of clouds or 'feel' it in the mugginess of the air.