Sentence:  The architects do not believe that the education of the interior designer is sufficiently good or sufficiently extended to compare with that of the architect and that , therefore , the interior designer <WSD>is</WSD> incapable of understanding the architectural principles involved in planning the interior of a building . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)