Sentence:  In order to understand the marked contract between Comte's mental attitude during his early years and that of his later life, we must keep in mind Jung's hypothesis of the two psychological types, the <WSD>introvert</WSD> and extrovert,—the thinking type and the feeling type. 
Meaning of the word marked with <WSD> tags:  An introverted person: one who is considered more thoughtful than social, with a personality more inwardly than outwardly directed; one who often prefers to have time in non-social situations.