Here we have the distinction already noticed.The so-called 'thing'may be merely a collection of separate things,and we can discover the 'laws'applicable to all by combining the laws applicable to each.From a given 'collocation'we can infer past or future 'collocations,'and one set of results can be added to or superposed upon the other.But when we proceed to chemical or organic compounds,we have 'heteropathic'laws.The compound may be analysed into elements,but we cannot derive the properties of the compounds from the properties of the elements.Hydrogen and oxygen can be combined into the form of water;but we could not infer the properties of water from the properties of the hydrogen and oxygen taken apart.In organic compounds,the problem is still more intricate.We have to consider a series of inter-related changes taking place within the organism,and dependent partly upon the 'environment'and partly upon the complex constitution of the organism itself.It is a unit in so far as all its properties manifest an organic law or a system of organic laws.Individuals may differ from external causes as plants,for example,in different soils,and in that case we may regard the differences as simply derivative.Differences which belong to the organic law itself indicate differences of kind;and these are ultimate for us,so long as we cannot trace the way in which they are dependent upon differences of constitution.
These,roughly stated,are the facts which Mill recognises.Now,in any case whatever,we can only 'explain'a fact by assuming both 'collocation'and 'causation';or,in other words,we must have a statement of facts and of laws.Our analysis of the phenomena will in all cases come to showing how a given state results from,or results in,a previous or succeeding state.If new properties appear from the combination of simpler elements,we should infer that they result,though we may be quite unable in the existing state of knowledge to show how they result,from the properties of those elements.The properties do not manifest themselves,and are therefore not discoverable,till the combination is formed;and are thus only known to us 'empirically.'No process of reasoning,that is,can be adduced to show that they must result from the combination.But,in the case supposed,we do not doubt that they do result,and we assume that the elements had certain latent properties not previously discoverable.This,however,is the point upon which Mill diverges,owing,as I think,to his imperfect view of causation.
The doctrine of 'kinds,'in fact,gives the answer to Mill's old problem,why a single instance is sometimes conclusive,whereas any number of instances may sometimes fail to give certainty.It is this reciprocal connection between the properties of a 'kind'which justifies the inference from one set of attributes to another attribute --the inference implied in all induction.But Mill's interpretation of the fact seems strangely inconsistent.His favourite instance is the black crow.
I have seen a million black crows.Can I say that the million and oneth crow will be black?To answer this we must ask whether blackness is a property of 'kind.'(79)If the blackness be,'as it were,an accident,'or not a property of kind,it must,he says,be a case of causation.If not a case of causation,it must be a property of kind.Hence we have the singular result,that if the coexistence be casual,it is caused,and if invariable,not caused.As 'causation'means according to him simply unconditional connection,the statement seems to be especially paradoxical.It is,however,explicable.
The blackness of the crow may be regarded as 'accidental,'if it is due to the external cause.The crow,perhaps,has fallen into a paint-pot.The blackness is 'caused,'then,by the properties of paint and by the 'accidental'collocation.It is an 'accident'in the crow,though caused in respect of the general arrangements of the universe.But why,if a property of 'kind,'should it be called 'not caused'?Here we have a curious result of Mill's view of causation.Our natural reply would be that the colour is still caused as everything else is caused.(80)We assume,that is,that 'crow'implies such a constitution that under a given environment crows will be black.Change something outside the crow and he may turn white.Or find a white crow in the same 'environment,'and we infer some difference in his constitution.There is a relation,we assume,though we cannot specify its nature,which determines the colour,and as in all cases we have at once collocation and causation.Here is Mill's peculiar difficulty.Causation,as he is profoundly convinced,always means a beginning.It is only,as we have seen,concerned with changes,not with persistence.Therefore,if two things,like blackness and crowness,exist side by side,it is a case of collocation,and consequently,as he supposes,not a case of causation.He cannot recognise a reciprocal relation,although it is clear that if one thing is found always to accompany another,the argument is the same as though one always followed another.
