David Hume (1711-1776) took Gottfried Leibbniz's fork and added a prong.

Every Statement Can Be Put Into One Of Three Categories

1. True or False by definition.

2. Dependant on experience.

3. Nonsense

(1) The statement "1+1=2" is true by definition. The number '2' is just another way to express the statement '1 and another 1'; it doesn't add anything to the idea of '1 +1'.

(2) The statement "Bill Gates is rich" is based on experience, not logic. Bill Gates could be poor and still be Bill Gates. (While '1+1' could not equal '4' and still be '1+1')

(3) There are some things that don't fit into these two categories. These, according to Hume are stuff and nonsense. "Dragons fly" is not factual, and therefor a bad thing*.

In Hume's view only the second category is worth looking at, as it is the only set of new, useful information. As far as he was concerned the terms 'real knowledge' and 'synthetic statement' are equal.

This bit of nonsense started empiricism, notable for pointing out that the statement 'God exists' fell into the nonsense category.

Take a gander at Hume's Maxim.

*A quote from Hume on the subject nonsense and books containing such: "Commit it all then to flames, for it can contain nothing but sophistry and illusion".