He describes the five basic principles of induction which have come to be known as Mill's Methods--the method of agreement, the method of difference
, the joint or double method of agreement and difference, the method of residues, and the method of concomitant variations.
Much of this work explicitly or implicitly relies on the comparative method of analysis which Skocpol and Margaret Somers note are essentially of two forms: what they call the "Method of Agreement" between two societies where the outcome is the same, but most institutions were different, and the "Method of Difference
" where all but one of the causal factors or institutions were the same in two societies, and their outcome was different.
To apply this proposed framework to the Iranian case, Zahedi uses a comparative methodology termed by John Stuart Mill as "the method of difference
37) states it, "There is another problem with the method of agreement that is particularly relevant to comparative social science: the method of agreement is completely incapacitated by multiple causation (which was know to Mill as plural causation)." We could not rely on Mill's "method of difference" either, because it involves comparing cases that differ on only one potential condition, which can be inferred to be causal.
By the logic of comparisons, using Mill's "method of agreement" and "method of difference" (see Lieberson 1992), inferences can be made from one case to another about potentially spurious relationships (the correlation between X and Y is because both X and Y are strongly correlated with a third variable, M).
Future research on political violence committed by social movements may benefit from an application of Mill's method of difference
. As della Porta points out, the employment of the method of agreement may potentially limit her findings.
In fact the essence of the method of differences for the solution of differential equations is that instead of solving a differential equation one solves a corresponding finite difference equation that is obtained by substituting differences expressions with higher or lower level of accuracy for the derivatives.
The method of differences is especially suitable for the solution of boundary value problems, for instance, the problem of determining a function that satisfies the Laplace equation in the interior of a given field [OMEGA] and possesses given values at the boundary of the field; such problems arise in the exploration of stationary temperature distribution when the temperature at the boundary of the field is known, in investigating the tension in a twisted rod of prismatic section, etc.
Each country studied in the papers differs from the others in some respects, providing the variation necessary to account for the differences in response, but all have an underlying unity due to their common European heritage, permitting something like an application of John Stuart Mill's "Method of Differences
" or ceteris paribus experiment.