“Subduct from any given phenomenon such part as is known by previous induction to be the effect of certain antecedents and the residue of the phenomenon is the effect of the remaining antecedents”.
The significance of this method is that this method is applied in the complex cases. It is applied only in such complex cases where the causal relationships of the contained factors are known excluding one. Only in such cases the causal relationship between the remaining factors are established. *
Symbolical example:
ABC is followed by xyz
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BC is known to be casually connected with yz
\ A is the cause of a
This method applies the new principle of elimination added by Joseph. It follows the principle; nothing is the cause of a phenomenon which is known to be the cause of a different phenomenon.
In the above example since y and z are known to be related with B and C, y and z cannot be causally connected with A. Hence the remaining one x is causally connected with A.
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Concrete examples:
1. The cost of three articles A, B and C is Rs. 100/-. It is known that the cost of B is
Rs. 35/- and C is Rs. 25/-. It is obvious that the cost of A is Rs. 40/- which is the subduct of B and C from ABC.
2. A shopkeeper wants to know the weight of the oil in a container. He weighs it and from that weight deducts the weight of the empty container. That helps him to determine the weight of the oil.
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Characteristics:
This method is said to be a method of discovery. In a complex situation when some part of the phenomenon is not explained by the known causes this method may help to find out a further cause to explain the whole phenomenon. Mellone says that it is a “Finger post of the unexplained”.
Argon, a gas, was discovered by help of this method. When nitrogen gas collected from the atmosphere was found heavier than the nitrogen prepared in the laboratory, it was assumed that some gas might be mixed up with atmospheric nitrogen and by this method argon was discovered.
It is considered as the modification of the method of difference. Because both the methods employ only two instances. But this view does not seem to be proper for the reason that the method of residues is a deductive method but the method of difference cannot be considered as a deductive method.
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Method of difference obtains the negative instance by observation or experiment, as the case may be, but the method of residues obtains the negative instance by prior induction.
The method of residues is essentially a method of deduction. One can clearly notice in this case that the knowledge obtained is deducted from the total observational knowledge in order to get the conclusion.
One only follows a method of deduction to reach at the conclusion. In the symbolical example we have deducted BC and xy from ABC and xyz respectively to get the relation between A and x. For this reason it is considered as a deductive method.
Since we adopt the method of subtraction, it is claimed to be a deductive method. But primarily it is an induction because the method of subtraction is applied only to the cases of two observational instances.
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The method of residues holds good only when there is some prior knowledge of causation. In no other method of experimental inquiry there is the essential need of some prior causal knowledge.
Along with the previous knowledge if something more “is found as unexplained, it takes the shape of a hypothesis. An attempt to explain this unexplained factor leads to the application of this method. Thus this method holds good only when there is some prior knowledge of causation.
There was the knowledge about the path of movement of Uranus. But when was Uranus found to deviate from its calculated path, the cause of the deviation was suspected and the hypothesis was framed that the deviation might be due to some other planet. Infect, it helped in the discovery of the planet Neptune in this manner.
It is considered as the application of the method of residues for the reason that the effect of the known planet was deducted from the total effect of gravitational pull of Uranus. The trial to solve the hypothesis helped to find out the causal relationship.
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Advantages:
1. This method is used is advanced stage of scientific analysis. When in scientific analysis the data are collected by experiment the method of residues helps in ascertaing a causal relationship between two phenomena.
2. It follows the method of experiment. So its finding is highly probable. It has the advantages of experiment.
3. It can deal with complex phenomenon. Especially the method-is useful in case of intermixture of effects.
Disadvantages:
1. Without previous knowledge of causal relation the method of residues cannot be applied.
2. If the complex effect cannot be reduced or analyzed, then this method cannot be applied.
3. This method may confuse an irrelevant factor to be the cause.