Here is a quote by Kronecker
>I recognize a true scientific value - in
the field of mathematics - only in concrete mathematical truths, or, to put it more
pointedly, only in mathematical formulas. These, as the history of mathematics shows,
are the only essential thing. The various theories regarding the foundations of mathematics (such as that of Lagrange) have over time fallen by the wayside, but the Lagrange resolvent remains.
So apparently Lagrange has developed some kind of foundations of mathematics, but I can't find anything about it. Does anyone know what his foundations looked like?