Friedrich (Frederick) Engels:

Feuerbach—The Roots of Socialist Philosophy

And:
Theses on Feuerbach. By Karl Marx.
104 pages.

1. Book version: ISBN 9781595691286 or PayPal. 5.5 x 8.5 in

2. eBook version: Google Play

"This work is a testimony with regard to the method employed by Marx and Engels in arriving at their philosophical conclusions. It is the statement of the philosophical foundations of modern socialism by one who helped to lay them; it is an old man's account of the case upon the preparation of which he has spent his entire life, for, this work, short as it is, represents the results of forty years of toil and persevering effort." [Austin Lewis]

"Marx has died without either of us having had an opportunity of coming back to the antithesis... We never came back to Feuerbach, who occupies an intermediate position between the philosophy of Hegel and our own... Under these circumstances a short, compact explanation of our relations to the Hegelian philosophy, of our going forth and departure from it, appears to me to be more and more required. And just in the same way a full recognition of the influence which Feuerbach, more than all the other post-Hegelian philosophers, had over us, during the period of our youthful enthusiasm, presents itself to me as an unendurable debt of hono ... On the other hand, I have found in an old volume of Marx the eleven essays on Feuerbach printed here as an appendix. These are notes hurriedly scribbled in for later elaboration, not in the least degree prepared for the press, but invaluable, as the first written form, in which is planted the genial germ of the new philosophy." [Friedrich Engels]