I doubt not, but from self-evident Propositions, by necessary Consequences, as incontestable as those in Mathematics, the measures of right and wrong… - John Locke

It is ambition enough to be employed as an under-labourer in clearing the ground a little, and removing some of the rubbish which lies in the way to knowledge.

One thing I have frequently observed in children, that when they have got possession of any poor creature, they are apt to use it ill: they often torment, and treat it very roughly, young birds, butterflies, and such other poor animals which fall into their hands, and that with a seeming kind of pleasure. This I think should be watched in them, and if they incline to any such cruelty, they should be taught the contrary usage. For the custom of tormenting and killing of beasts, will, by degrees, harden their minds even towards men; and they will delight in the suffering and destruction of inferior creatures, will not be apt to be very compassionate or benign to those of their own kind. Our practice takes notice of this in the exclusion of butchers from juries of life and death.

I am sure the principal end why we are to get knowledge here, is to make use of it for the benefit of ourselves and others in this world; but if by gaining it we destroy our health, we labour for a thing that will be useless in our hands, and if by harnessing our bodies (though with a design to render ourselves more useful) we deprive ourselves of the abilities and opportunities of doing that good we might have done with a meaner talent, which God thought sufficient for us by having denied us the strength to improve it to that pitch which men of higher constitutions can attain to, we rob God of so much service, and our neighbor of all that help, which, in a state of health, with moderate knowledge, we might have been able to perform. He that sinks his vessel by overloading it, though it be with gold and silver and precious stones, will gives his owner but an ill account of his voyage.