Sentence:  The concept of unity , in which positive and negative are attributes of the same force , in which good and evil are relative , ever-changing , and always <WSD>joined</WSD> 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:  of or relating to two people who are married to each other