Its being put together again rightly would be a proof that it had been taken to pieces rightly.
And so with Master Analysis.

If he can take a thing to pieces so that his brother Synthesis can put it together again, you may be sure that he has done his work rightly.
Now he can take a bit of chalk to pieces, so that it shall become several different things, none of which is chalk, or like chalk at all.

And then his brother Synthesis can put them together again, so that they shall become chalk, as they were before.

He can do that very nearly, but not quite.

There is, in every average piece of chalk, something which he cannot make into chalk again when he has once unmade it.
What that is I will show you presently; and a wonderful tale hangs thereby.