Friedrich Engels,
Landmarks of Scientific Socialism…
“ The enemy which Engels was most anxious to dislodge was "mechanical socialism," a naïve invention of a perfect system capable of withstanding the ravages of time, because founded upon eternal principles of truth and justice. That enemy has now obeyed the law of the dialectic and passed away. Nobody builds such systems, nowadays. They have ceased their building however not in obedience to the commands of Friedrich Engels but because the lapse of time and the change in conditions have proved the dialectic to the revolutionist. ”
