1. No one supposes that a good induction can be arrived at merely by counting cases. The business of strengthening the argument chiefly consists in determing whether the alleged association is stable, when the accompanying conditions are varied. This process of improving the analogy, as I have called it in Part III, is, both logically and practically, of the essence of the argument.

Now in statistical reasoning (or inductive correlation) that part of the argument, which corresponds to counting the cases in inductive generalisation, may present considerable technical difficulty. This is especially so in the particularly complex cases of what in the next chapter (§ 9), I shall term quantitative correlation, which have greatly occupied the attention of English statisticians in recent years. But clearly it would be an error to suppose that, when we have successfully overcome the mathematical or other technical difficulties, we have made any greater progress towards establishing our conclusion than when, in the case of inductive generalisation, we have counted the cases but have not yet analysed or compared the descriptive and nonnumerical differences and resemblances. In order to get a good scientific argument we still have to pursue precisely the same scientific methods of experiment, analysis, comparison, and differentiation as are recognised to be necessary to establish any scientific generalisation. These methods are not reducible to a precise mathematical form for the reasons examined in Part III of this treatise.