We are, Secondly, to gain all we can without hurting our mind any more than our body. For neither may we hurt this. We must preserve, at all events, the spirit of an healthful mind.
Therefore we may not engage or continue in any sinful trade, any that is contrary to the law of God, or of our country. Such are all that necessarily imply our robbing or defrauding the king of his lawful customs. For it is at least as sinful to defraud the king of his right, as to rob our fellow subjects. And the king has full as much right, to his customs as we have to our houses and apparel.
Other businesses there are, which however innocent in themselves, cannot be followed with innocence now at least, not in England; such, for instance, as will not afford a competent maintenance without cheating or lying, or conformity to some custom which not consistent with a good conscience: These, likewise, are sacredly to be avoided, whatever gain they may be attended with provided we follow the custom of the trade; for to gain money we must not lose our souls.
There are yet others which many pursue with perfect innocence, without hurting either their body or mind; And yet perhaps you cannot: Either they may entangle you in that company which would destroy your soul; and by repeated experiments it may appear that you cannot separate the one from the other; or there may be an idiosyncrasy, — a peculiarity in your constitution of soul, (as there is in the bodily constitution of many,) by reason whereof that employment is deadly to you, which another may safely follow.
So I am convinced, from many experiments, I could not study, to any degree of perfection, either mathematics, arithmetic, or algebra, without being a Deist, if not an Atheist: And yet others may study them all their lives without sustaining any inconvenience. None therefore can here determine for another; but every man must judge for himself, and abstain from whatever he in particular finds to be hurtful to his soul.