I recieved exactly a week ago your favor of Dec. 31. which may explain the tardy date of this acknolegement, and of my thanks for the copy of your Inquiries concerning the laws of nature, which accompanied it. on these you ask my observations, ‘as well on their errors, as on what I may approve.’ the range of these enquiries takes in the whole field of physics, and also of Medecine and it’s kindred sciences. on the last I could offer nothing new to one of the faculty: and as to Physics I percieve that many of the fundamental principles, heretofore supposed established, are deemed erroneous, and others proposed as substitutes. I am an advocate for freedom of challenge of every fact and principle which any one may suspect to be founded in error. one man’s opinion being as free as another’s, neither is to controul or to be controuled by the other. on the contrary, the freer the enquiry, the more favorable to truth. but when a whole system is proposed to be reformed, the undertaking is for the young, not for the old. the latter have not time to resume their enquiries de novo, and to learn over again all the lessons they have learnt in their preceding life. having once fully enquired, and maturely made up their minds, they must leave to future investigators the advantages of correcting, or of still further advancing the boundaries of science. it has been said, as you know, that no physician in Europe, then 40. years of age, ever became a convert to Harvey’s discovery of the circulation of the blood. but I, my good Sir, am 73. I have not then either time or energy enough to undertake the settlement of new questions, or the correction of old ones: and while I give you credit for the freedom & ingenuity of the ideas I find in your book, I am sure of your permission to leave them to younger & more vigorous minds for scrutiny at the bar of reason & fact. I hope you will be so good as to accept of this apology for my declining to say any thing, yea, or nay, on these profound subjects.   On that of the Long talk which accompanied the other publication I am happy to percieve that what has been the creed of my youth, and is now matured by age, has the further sanction of your sentiments, for which, on this as well as the other subjects, I tender you the assurance of my high respect.

Th: Jefferson