Sentence:  If a man's deep and conscientious regard for the truth be such that he cannot, consistently with the requisitions of his moral nature, repeat to others mere <WSD>vaguenesses</WSD> and uncertainties, he will naturally give such strict and serious attention to the present objects of inquiry and knowledge, that they will remain in his memory afterward with remarkable distinctness and permanency. 
Meaning of the word marked with <WSD> tags:  Something which is vague, or an instance or example of vagueness.