Sec. 2.  Secondary Laws may also be classified according to their constancy into—­(1) the Invariable (as far as experience reaches), and (2) Approximate Generalisations in the form—­Most X’s are Y. Of the invariable we have given examples above.  The following are approximate generalisations:  Most comets go round the Sun from East to West; Most metals are solid at ordinary temperatures; Most marsupials are Australasian; Most arctic animals are white in winter; Most cases of plague are fatal; Most men think first of their own interests.  Some of these laws are empirical, as that ’Most metals are solid at ordinary temperatures’:  at present no reason can be given for this; nor do we know why most cases of plague are fatal.  Others, however, are at least partially derivative, as that ‘Most arctic animals are white’; for this seems to be due to the advantage of concealment in the snow; whether, as with the bear, the better to surprise its prey, or, with the hare, to escape the notice of its enemies.

But the scientific treatment of such a proposition requires that we should also explain the exceptions:  if ‘Most are,’ this implies that ‘Some are not’; why not, then?  Now, if we can give reasons for all the exceptions, the approximate generalisation may be converted into an universal one, thus:  ’All arctic animals are white, unless (like the raven) they need no concealment either to prey or to escape; or unless mutual recognition is more important to them than concealment (as with the musk-sheep)’.  The same end of universal statement may be gained by including the conditions on which the phenomenon depends, thus:  ’All arctic animals to whom concealment is of the utmost utility are white.’

When statistics are obtainable, it is proper to convert an approximate generalisation into a proportional statement of the fact, thus:  instead of ‘Most attacks of plague are fatal’, we might find that in a certain country 70 per cent. were so.  Then, if we found that in another country the percentage of deaths was 60, in another 40, we might discover, in the different conditions of these countries, a clue to the high rate of mortality from this disease.  Even if the proportion of cases in which two facts are connected does not amount to ‘Most,’ yet, if any definite percentage is obtainable, the proposition has a higher scientific value than a vague ‘Some’:  as if we know that 2 per cent. of the deaths in England are due to suicide, this may be compared with the rates of suicide in other countries; from which perhaps inferences may be drawn as to the causes of suicide.

In one department of life, namely, Politics, there is a special advantage in true approximate generalisations amounting to ‘Most cases.’  The citizens of any State are so various in character, enlightenment, and conditions of life, that we can expect to find few propositions universally true of them:  so that propositions true of the majority must be trusted as the bases of legislation.  If most men are deterred from crime by fear of punishment; if most men will idle if they can obtain support without industry; if most jurymen will refuse to convict of a crime for which the prescribed penalties seem to them too severe; these are most useful truths, though there should be numerous exceptions to them all.