To apply this distinction to the things of Logic:  it is easy to see how two propositions may have the same Form but different Matter:  not using ‘Form’ in the sense of ‘shape,’ but for that which is common to many things, in contrast with that which is peculiar to each.  Thus, All male lions are tawny and All water is liquid at 50 deg.  Fahrenheit, are two propositions that have the same form, though their matter is entirely different.  They both predicate something of the whole of their subjects, though their subjects are different, and so are the things predicated of them.  Again, All male lions have tufted tails and All male lions have manes, are two propositions having the same form and, in their subjects, the same matter, but different matter in their predicates.  If, however, we take two such propositions as these:  All male lions have manes and Some male lions have manes, here the matter is the same in both, but the form is different—­in the first, predication is made concerning every male lion; in the second of only some male lions; the first is universal, the second is particular.  Or, again, if we take Some tigers are man-eaters and Some tigers are not man-eaters, here too the matter is the same, but the form is different; for the first proposition is affirmative, whilst the second is negative.

Sec. 6.  Now, according to Hamilton and Whately, pure Logic has to do only with the Form of propositions and arguments.  As to their Matter, whether they are really true in fact, that is a question, they said, not for Logic, but for experience, or for the special sciences.  But Mill desired so to extend logical method as to test the material truth of propositions:  he thought that he could expound a method by which experience itself and the conclusions of the special sciences may be examined.

To this method it may be objected, that the claim to determine Material Truth takes for granted that the order of Nature will remain unchanged, that (for example) water not only at present is a liquid at 50 deg.  Fahrenheit, but will always be so; whereas (although we have no reason to expect such a thing) the order of Nature may alter—­it is at least supposable—­and in that event water may freeze at such a temperature.  Any matter of fact, again, must depend on observation, either directly, or by inference—­as when something is asserted about atoms or ether.  But observation and material inference are subject to the limitations of our faculties; and however we may aid observation by microscopes and micrometers, it is still observation; and however we may correct our observations by repetition, comparison and refined mathematical methods of making allowances, the correction of error is only an approximation to accuracy.  Outside of Formal Reasoning, suspense of judgment is your only attitude.