Seventeenth-century philosopher John Locke stated that as much as 99 percent of the value of any useful product can be attributed to "the effects of labor." For Locke's intellectual heirs it was only a short step to the "labor theory of value," whose formulators held that 100 percent of the value of any product is generated by labor (the human work needed to produce goods) and that therefore the employer who appropriates any part of the product's value as profit is practicing theft.

    Although human effort is required to produce goods for the consumer market, effort is also invested in making capital goods (tools, machines, etc.), which are used to facilitate the production of consumer goods. In modern economies about one-third of the total output of consumer goods is attributable to the use of capital goods. Approximately two-thirds of the income derived from this total output is paid out to workers as wages and salaries, the remaining third serving as compensation to the owners of the capital goods. Moreover, part of this remaining third is received by workers who are shareholders, pension beneficiaries, and the like. The labor theory of value systematically disregards the productive contribution of capital goods—a failing for which Locke must bear part of the blame.

Line	In 1971 researchers hoping to predict earthquakes in
	the short term by identifying precursory phenomena
	(those that occur a few days before large quakes
	but not otherwise) turned their attention to changes
(5)	in seismic waves that had been detected prior to
	earthquakes. An explanation for such changes was
	offered by “dilatancy theory,” based on a well-known
	phenomenon observed in rocks in the laboratory:
	as stress builds, microfractures in rock close,
(10)	decreasing the rock’s volume. But as stress
	continues to increase, the rock begins to crack and
	expand in volume, allowing groundwater to seep in,
	weakening the rock. According to this theory, such
	effects could lead to several precursory phenomena in
(15)	the field, including a change in the velocity of seismic
	waves, and an increase in small, nearby tremors.
	Researchers initially reported success in identifying
	these possible precursors, but subsequent analyses
	of their data proved disheartening. Seismic waves
(20)	with unusual velocities were recorded before some
	earthquakes, but while the historical record confirms
	that most large earthquakes are preceded by minor
	tremors, these foreshocks indicate nothing about
	the magnitude of an impending quake and are
(25)	indistinguishable from other minor tremors that occur
	without large earthquakes.
	In the 1980s, some researchers turned their
	efforts from short-term to long-term prediction.
	Noting that earthquakes tend to occur repeatedly in
(30)	certain regions, Lindh and Baker attempted to identify
	patterns of recurrence, or earthquake cycles, on which
	to base predictions. In a study of earthquake-prone
	sites along the San Andreas Fault, they determined
	that quakes occurred at intervals of approximately 22
(35)	years near one site and concluded that there was a
	95 percent probability of an earthquake in that area
	by 1992. The earthquake did not occur within the time
	frame predicted, however.
	Evidence against the kind of regular
(40)	earthquake cycles that Lindh and Baker tried
	to establish has come from a relatively new
	field, paleoseismology. Paleoseismologists
	have unearthed and dated geological features
	such as fault scarps that were caused by
(45)	earthquakes thousands of years ago. They have
	determined that the average interval between ten
	earthquakes that took place at one site along the
	San Andreas Fault in the past two millennia was
	132 years, but individual intervals ranged greatly,
(50)	from 44 to 332 years.