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either carbons (C) or hydrogen (H), we shall only get a mixture of marsh gas and carbon or hydrogen. This will continue until we add a quantity corresponding to one atom of carbon and two of hydrogen, when the whole nature of the substance changes and we get a new gas, with new properties, acetylene, or C2, H6, and so forth. Quantity has changed into quality. Now let us take a simple example from physics. When water is healed it becomes warmer and warmer, but up to a certain point the difference is merely in the degree of heat: fundamentally the cold water and the hot water are still the same liquid, but when the heat applied reaches a certain quantity, 100°C or 212°F the water suddenly turns into a new substance—steam, a gas with quite different properties from water. Quantity has changed into quality. Now let us take one example from history. So long as the labourer was tied to the soil, so long did we have the form of society known as serfdom. But as production and commerce developed, so it gradually became more and more necessary to have free access to labour in certain areas which could only be obtained by allowing the labourer, or potential labourer to travel where work was to be found. Also, as the old processes and forms of agriculture either became obsolete or not so profitable to the landowners, the latter started to give their serfs either more freedom of movement or to convert their forced labour for them into money payments or rents. Thus gradually there developed all the conditions in society for the abolition of the system of serfdom, and when this development reached a certain stage, serfdom gave way to free private production. In some cases the change was brought about with much, in other cases with less, violence. In some cases the change was rapid; in others it was slow. But in all cases the change was a revolutionary one—a new form of society took the place of the old, because the new conditions necessitated this change.
We have no space to multiply these examples, as might be done from all the sciences and from all experiences in life. These laws and these methods of study Marx and Engels adopted from the Hegelian philosophy. But whilst they held fast to Hegel's dialectieal method they rejected
