The most significant use of feedback is undoubtedly related to automatic control. Its first technological applications, often unconscious, are very old and well documented. Here we develop some considerations on the reasons why the inventors of the oldest control systems might not have been fully aware of the feedback nature of their devices (for which feedback models have only recently been proposed to explain their operation) and the reasons why, instead, feedback has consciously been employed in the technical applications of electronics since the first decades of the 20th century (to modify the performance of amplifiers and oscillators); it is worth noting that the word feedback has been coined in those years. Furthermore, feedback is also effectively exploited in mathematics, in two distinct, yet related, fields: the algorithms whose flow-chart includes loops and the analog computation for solving ordinary differential equations. Finally, feedback is the key element of many explanatory models for phenomena studied by the physical and biological sciences, as well as by the sciences of man and society; the latter models often exhibit an intrinsic interest from a philosophical viewpoint too.
