Sentence:  A dominant <WSD>motive</WSD> is the poet 's longing for his homeland and its boyhood associations : `` Not men folk , but the fields where I would stray , The stones where as a child I used to play '' . 
Meaning of the word marked with <WSD> tags:  the psychological feature that arouses an organism to action toward a desired goal; the reason for the action; that which gives purpose and direction to behavior