Sentence:  It <WSD>is</WSD> quite probable , however , that stupidity , inexperience and childish adherence to slogans like `` unconditional surrender '' had more to do with the unsatisfactory settlements at the end of the war than treason or sympathy with Communism . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)