Sentence:  The concept of unity , in which positive and negative <WSD>are</WSD> attributes of the same force , in which good and evil are relative , ever-changing , and always joined to the same phenomenon - such a concept is still reserved to the physical sciences and to the few who have grasped the history of ideas . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)