This leads us directly into the next, and very important, objection.
"Far from being analytic, the propositions of arithmetic are not even true-at least not in all cases. Two and two doesn't always make four. For example, if you add two quarts of water to two quarts of alcohol, you ought(if the arithmetical proposition is true) to get four quarts-but you don't; you get a little less, owing to the interpenetration of molecules of the two substances.
If you put together two lions and two lambs. and turn your back for a moment, you will have not four things, but only two-two lions. When two amoebas subdivide, they become four-what was two is now four! How can arithmetical propositions be necessary at all, much less analytic, if they aren't even true in all cases-when reality often shows them to be false?"
But this objection is the result of a total misunderstanding. When we say that 2 plus 2 equals 4, we do not deny for a moment that what was two can become four (the amoebas), or that you can have four things at one time and have only two things at a later time (the lions and the lambs). It says only that if you that two and two, then at that moment you have four.
Arithmetic does not tell you anything about natural processes-how two things can become four thing, or how four thing can be reduced to two things. Arithmetic doesn't even tell you that there are four of anything in the world at all, or even that there is a world in which such distinctions can be made. It says only that if there are two, and then two more, then there must be four:
that to say there are two plus two and to say that there are four is to say the same thing. When there are two lions and two lambs, then there are four thing; when there are only teo lions, then there are only two-that is. one plus one-things gave rise to a million things, this would not violate "2 and 2 equals 4" or any other proposition of arithmetic. Two rabbits soon become a million
rabbits; and if two things exploded into a million things, or into nothing at all, this would not refute any law of arithmetic.
What turns into what, what becomes what, how one thing changes into another-all these are matters for the physical sciences to investigate; these are all a part of what happens in the world, and propositions about these things are all synthetic and contingent. But the propositions of arithmetic say nothing whatever about the changes that go on in nature; they say nothing at all about
the kind of a world we live in, nor would they be changed in the slightest if the world were quite different from what it is, for the laws of aritmetic do not describe what the world is like. Arithmetic doesn't even tell you that the number 4 applies to anything in the world, but only that if it applies, then "2 plus 2" also applies, because the two symbols mean the same thing.