Sentence:  Presumably , if the reverse is the case and the good effect <WSD>is</WSD> more certain than the evil result that may be forthcoming , not only must the good and the evil be prudentially weighed and found proportionate , but also calculation of the probabilities and of the degree of certainty or uncertainty in the good or evil effect must be taken into account . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)