A few definitions: FBW - Augmentation - Protection - Automation
I applaud the recent entries in this thread making the case that FBW and Automation are two different concepts. I would like to add a third term: augmentation. Here are the definitions of these three plus protection that I use. I have found these to be very helpful in explaining the evolution of and difference between airplane control systems.
Fly-By-Wire (FBW): This refers to the connection between pilot input and control surface motion as being other than a mechanical link. An airplane configured with electric sensors on the pilot's controls (sensing either force or position) and control surface positions commanded proportional to those pilot control positions has a FBW control system. The surfaces go where the pilot commands them such that the pilot to control surface linkage behaves the same as if mechanical linkages between the two were used. Most FBW control system are more complex than this, but strictly speaking this simple example qualifies as FBW.
Augmentation: This refers to the motion of the control surfaces being more than just a reflection of the pilot's controller positions. Yaw dampers are an example of early augmentation wherein the rudder command is the sum of the pilot command via the rudder pedals and the control system yaw damper command. Note that for this example, augmentation was introduced without FBW. More recent examples of airplanes with high degrees of augmentation are the A320 and later Airbus designs and the B777 and later Boeing designs. For these airplanes maneuver demand control is provided in one or more axis such that the pilot's controller position commands a maneuver (e.g., pitch rate, roll rate, sideslip angle) rather than a direct surface position or an addative increment in surface position. Augmentation allows for closed-loop (i.e., control system active) handling qualities to be different from those of the bare airplane. This allows for the airplane configuration to be optimized in the direction of improved performance at the expense of open-loop (or unaugmented) handling qualities. The control system augmentation enables configuration features that improve performance.
Protection: This refers to features of the control system that reduce the likelihood of operating near or beyond edges of the flight envelope that present degradation in airplane performance and/or controllability. Protection functions come in many forms. Some such as stick shakers and nudgers provide pilot awareness. Others such as angle-of-attack or bank angle limiters provide hard limits that the pilots are not able to command beyond. Similar to early examples of augmentation, early protection functions were introduced without FBW. The more elaborate protection functions found in recent airplane models require FBW in order to allow for control surface motions that differ significantly from the pilot control positions as observed on the flight deck.
Automation: This refers to the basic concepts of autopilot and autothrottle. With automation engaged, the pilot can go hand's off for extended periods of time. Autopilots and autothrottles were introduced to commercial airplanes long before FBW. For these systems the autopilot effectively moved the pilot's flight deck controls to provide commands to the surfaces and the engines in the manner that the pilot would when flying manually. With the introduction of FBW where there is no mechanical linkage between pilot controls and the surfaces or the engines it is possible to implement automation without motion of the pilot's controls. Airbus has chosen this simpler route such that the pilots controls are not driven to show autopilot and autothrottle commands when those automation functions are engaged. Boeing has chosen to actively back-drive the pilot controls when automation is engaged as a means of providing situational awareness to the flight deck crew as to what inputs the autopilot and autothrottle are making to the airplane.
I hope that these definitions help provide clarity to further discussions within this and other PPRUNE threads.