Sentence:  One might , indeed , argue that the history of <WSD>ideas</WSD> , in so far as it includes the literatures , must center on characterizations of human nature and that the great periods of literary achievement may be distinguished from one another by reference to the images of human nature that they succeed in fashioning . 
Meaning of the word marked with <WSD> tags:  the content of cognition; the main thing you are thinking about