If two or more instances of the phenomenon under investigation have only one circumstance in common, the circumstance in which alone all the instances agree, is the cause (or effect) of the given phenomenon.
The importance of this method as compared to the procedure, of simple enumeration. is that it seeks to identify the one and the only circumstance that is associated with the effect. It is not the observation of merely the conjunction of one phenomenon with another phenomenon for a number of times.
There is the need of examining the constituent factors involved with the instance about which a causal connection is suspected.
Among the antecedent factors and the consequent factors the presence of the single invariable factor is taken into account for the causal relationship.
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Obviously there is the need of more than two instances where the event occurs. In all those cases there should be only one circumstance common both in the antecedent and consequent side. For example, if it is noticed that in a village the’ villagers have become able to get very good crops and they ail have used a definite type of fertilizer for their cultivation then the causal connection between the two events may be thought of.
Here one can notice the agreement between using a particular fertilizer and getting good crops and on that basis of agreement the causal connection between the pair of events may be established.
Similarly noticing the presence of large number of coconut trees in the sea areas one can draw the conclusion that climate nearer to the sea is suitable for the better growth of coconut trees.
Symbolically the method of Agreement may be represented as:
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A B C M followed by x y z p
A C D G followed by x z s t
A E F D followed by x n r s
A and x are causally related.
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In the above example in the antecedent side A is common to all three cases. B is absent in the 2nd and 3rd instances, C are absent in the 3rd instance, D is absent in the 1st instance, E and F are absent in the 1st and 2nd instances, M is absent in two other instance: So the three instances agree in respect of the occurrence of A in the antecedent side.
Similar x is common to all the three instances of consequent side. On this agreement it can be said that A is either the cause or a part of the cause of x.
This method is based on the first principle of elimination i.e. “whatever antecedes can be left out without prejudice to the effect can be no part of the cause”.
The significance of this principle is that if after taking away some circumstance still the effect is present” then that circumstance cannot be the cause.
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In other words a circumstar in the absence which the effect occurs cannot be the cause. Basing on this principle B, C, M, G, E, F, cannot be the cause.
Let us take some concrete example. By reading the books published by the Bureau of Textbook Preparation if a number of students achieve success in examinations, other conditions remaining variable; it will be presumed that the success of students may be d to their reading of the books of the Bureau of Textbook Preparation.
From a dental survey it was seen that in some particular cities the dental decay was remarkably’ low. After further investigation it was found that in their water supplies there was high level of fluoride. Thus it was supposed that the use of fluoride water is causally connected with the decrease of dental decay.
Characteristics
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1. It is a method of single agreement. Mellone and Coffey call this method as the method of single agreement. Here there is agreement in one circumstance only. Other circumstances differ in the instances.
In the case of more than one agreement this method is ineffective. The singleness of the agreement gives the impression of a causal relation
2. It is a method of observation. Through the observation of a number of instances where the common factor of agreement is found the causal connection can be established. Ii; is primarily a method of observation. But it does not mean that it is not applicable to experimental cases.
3. It is a method of discovery rather than a method of proof. Observation is a guide to discover something rather than to prove something. Since the method is a method of observation; it is a method of discovery.
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Through this method a causal connection is discovered between two phenomena because of their simultaneous occurrences. When two phenomena occur simultaneously it gives the impression that there might be a causal link between them.