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termed a law. Thus it is a law of nature that air has weight, that 
all men die, and the like. But, as the order of succession is logi- 
cally a fixed and necessary order, so the law which represents or 
expresses the order is logically a necessary law In this attribute 
of fixedness the mind recognises a resemblance between the order 
and the law which expresses it, so that as to the quality of necessity 
and fixedness, the law and the order are convertible things, and 
the law stands for the order. 
Force is a word arising out of man’s experience of this necessary 
order of events. He finds the fixed order to be an inevitable order, 
and this idea of inevitableness implies logically an irresistible force 
or power which compels to or maintains the order. Hence, cor- 
relative with order and law there is a conception of the power or 
force upon which the inevitableness of the order depends. In this 
way law and force become in language convertible terms ; and we 
speak equally of the law of gravity and the force of gravity, — the 
laws of attraction and the force of attraction ; and we say generally 
of a thing, that it has the force of law. Nevertheless, the term 
force has its own meaning, and specially includes or expresses the 
idea of causation independently of inevitableness^. In its strictest 
sense it is that which compels to the course of events expressed in 
the law without reference to the formula or the order. Yet the 
term is used correlatively with the order expressed ; so that order, 
law, and force equally express the same ideas of uniform sequence, 
fixedness, inevitableness, and an inevitably compelling force. Thus 
motion in a straight line implies both a force that impels, and an 
unchanging continuousness in the line of motion until an equal force 
interrupts or deflects. Starting from these generalizations of the 
words force and law, the author proceeds to show, that as the primary 
laws and forces are thus inevitable and fixed, the order which they 
compel and express can only be modified by equal forces acting 
according to like laws; since, logically, the inevitable alone can con- 
trol itself. Hence, he concludes, that all these phenomena of nature 
which appear to be deviations from the primary forces and laws of 
nature (as the resistance to the force of gravity which the upright 
position of man implies, and the like) are in fact due to laws and 
forces derivative from the primary, and which are therefore se- 
condary and contingent laws and forces. And since the phenomena 
of nature are all, in fact, deviations from one or two primary laws 
