Manuel DeLanda on Emergence, Causality and Realism

From The Speculative Turn (p.381-392):

Emergence, Causality and Realism

By Manuel DeLanda

"If a body is propelled in two directions by two forces, one tending to drive it to the north and the other to the east, it is caused to move in a given time exactly as far in both directions as the two forces would separately have carried it; and it is left precisely where it would have arrived if it had been acted upon first by one of the two forces, and afterwards by the other. [...] I shall give the name of the Composition of Causes to the principle which is exemplified in all cases in which the joint effect of several causes is identical with the sum of their separate effects. [...] This principle, however, by no means prevails in all departments of the field of nature. The chemical ombination of two substances produces, as is well known, a third substance with properties different from those of either of the two substances separately, or both of them taken together. Not a trace of the properties of hydrogen or of oxygen is observable in those of their compound, water."  — John Stuart Mill, A System of Logic

With these words John Stuart Mill began the modern debate on the question of emergence. While he himself did not use the term, one of its definitions, that of a property of a whole that is more than the sum of its parts, is clearly stated in this quote. Mill goes on to qualify this statement because two joint causes may interfere with each other and subtract rather than add their effects: a reservoir may be fed by a stream of water on one side while a drain empties it on the other side, the joint product being no change in the amount of water stored. Yet, for Mill, this is just another version of the Composition of Causes. So the real distinction between physical and chemical interactions is not so much that a joint effect is a mere sum but that it is entirely different or novel, ‘as in the experiment of two liquids which, when mixed in certain proportions, instantly become, not a larger amount of liquid, but a solid mass’. The term ‘emergent’ was introduced in 1875 by another philosopher, George Henry Lewes, also in the context of a discussion of joint causes and their effects. When two separate causes simply add or mix themselves in their joint effect, so that we can see their agency in action in that effect, the result is a mere ‘resultant’ but if there is novelty or heterogeneity in the effect then we may speak of an ‘emergent’.

Both authors viewed the difference between physics and chemistry as pivoting on the possibility of explanation: while in physics to explain an effect is to deduce it from a law, in chemistry deduction is not possible because of the existence of novelty in the effect. To know what effect the combination of two causes will have, what molecule will be synthesized from the interaction of two different atoms, for example, one needs to actually carry out an experiment. Mill did not think that this was a cause for despair: in due time chemical laws could be discovered that made the properties of water, for instance, deducible from those of oxygen and hydrogen. But to Lewes this possibility implied that water would cease to be an emergent and would become a resultant. As he wrote: ‘Some day, perhaps, we shall be able to express the unseen process in a mathematical formula; till then we must regard the water as an emergent’. In other words, something is an emergent only to the extent that we cannot deduce it from a law, and it ceases to be so the moment a law becomes available. This is an unfortunate conclusion, one that involves a serious misunderstanding of the nature of explanation in general and of causal explanation in particular.

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