Sentence:  But these scruples, if not too intricate, are of too extensive consideration for my present purpose, nor are they such as generally occur in common life; and though casuistical knowledge be useful in proper hands, yet it ought by no means to be carelessly exposed, since most will use it rather to lull than awaken their own consciences; and the threads of reasoning, on which truth is suspended, are frequently drawn to such <WSD>subtility</WSD>, that common eyes cannot perceive, and common sensibility cannot feel them. 18. 
Meaning of the word marked with <WSD> tags:  Excessive refinement of argument; casuistry.