Sentence:  ... the wise and considerate Men of the World, by a right and careful employment of their Thoughts, and Reason, attained true Notions in this, as well as other things; whilst the lazy and <WSD>inconsiderate</WSD> part of Men, making the far greater number, took up their Notions, by chance, from common Tradition, and vulgar Conceptions, without much beating their heads about them. 
Meaning of the word marked with <WSD> tags:  Not giving enough consideration to one's actions, conclusions, etc.; acting too quickly without considering the risks and consequences.