December 29, 1943

Dr. T. Addis

Stanford University

School of Medicine

2398 Sacramento Street

San Francisco, California

Dear Tom:

I have read carefully the quotation in your letter of December 22 from the book "Philosophical Method" by Collingwood. I have never thought much about philosophy, and perhaps if I had a better background his statements would seen more to me.

My interpretation of Collingwood's statements may be faulty because I can not tell from this brief excerpt from his writing what words he has taken to represent undefined concepts, and which words he has defined in terms of these concepts. It seems to me that Collingwood speaks very loosely: thus in his second sentence he says that ice, water, and steam differ both in degree, as hotter or colder, and in kind, as specifically different states of the same body; but in my opinion the second part of this statement has no meaning, since every difference between ice and water or water and steam is only a difference in degree: ice is less dense than water, it is harder than water, its vapor pressure is different from that of water, and so on.

I do not understand what Collingwood means by the generic essence of ice, water, and steam, unless he refers to conservation of mass or to the existence of molecules. Modem physical scientists try to avoid talking about anything except experiments and experimental results. One experiment which may be related to the generic essence is that one gram of ice can be converted completely into one gram of water or into one gram of steam—whether or not this shows that ice, water, and steam have a generic essence is not clear to me. Ammonium chloride can be converted by heating into a gaseous mixture of ammonia and hydrogen chloride; I am not sure that Collingwood would say that solid ammonium chloride and the gaseous mixture of ammonia and hydrogen chloride have a generic essence in common or not. Collingwood's final statement about all three forms being equally forms of water, each fully entitled to that name and all it implies, means very little to me, in terms of experimental operations, because I do not know what the term water implies other than the properties of ice, water, and water vapor, and the fact that the three phases are interconvertible.

If I were ever to be in an argument with anyone as to whether there is a change in the "generic essence" of H₂O on going from absolute zero to 100°C. I would require first that a definition of the term "generic essence" be given. So long as this term has not been rigorously defined discussion of it is a waste of effort.

Dr. Campbell and I think that the copper sulfate method of determining serum protein might be useful in connection with our animal work; could you tell me the title of the Rockefeller Institute publication on this subject which you showed me, and tell me where we should write for a copy?

I enjoyed my day with you very much, Please tell Mrs. Addis that I thank her for having me to dinner, and that, when I counted up my grams of protein for the day, I saw that I should have taken her advice in accepting the baked apple for dessert instead of pudding.

Sincerely yours,

Linus Pauling

LP:jr