Where the control loop Analogy Breaks

Calling feedback a control loop is useful for about five minutes. The comparison can expose structure that ordinary language hides. The problem begins when the comparison stops behaving like a tool and starts behaving like a claim about what the thing literally is.

Feedback is one of the strongest bridges between engineering and biology because both genuinely analyze sensing, response, delay, gain and stability.

What the metaphor gets right

Feedback is one of the strongest bridges between engineering and biology because both genuinely analyze sensing, response, delay, gain and stability.

This is why engineering metaphors are so attractive. They compress a complicated relationship into something we can manipulate mentally. In the best case, the metaphor produces predictions and sharper questions.

What it smuggles in

Real biological and social loops evolve, overlap and change their own parameters. A tidy block diagram can hide the physical mechanism and timescale of each connection.

Engineering words often carry hidden assumptions: a designer, a specification, modular ownership, explicit goals, a stable machine underneath the program. Those assumptions must be tested rather than inherited.

Return to the physical story

Feedback occurs when the consequences of a process alter its future behavior. Negative feedback can stabilize; positive feedback can amplify; delays and nonlinear responses can generate oscillation or instability.

Once the mechanism is back in view, the analogy can be kept on a short leash. We can state which relation is genuinely similar and which difference would make the analogy generate a wrong prediction.

My three tests for a metaphor

1. What mechanism does this comparison help me see?
2. Which engineering assumption does the natural system not share?
3. What would I predict incorrectly if I took the comparison literally?

The third test is the most important. An analogy that cannot fail is decoration, not explanation.

Beyond the borrowed language

Cybernetics made feedback a cross-disciplinary language for machines, organisms and communication, sometimes precisely and sometimes too loosely.

Feedback replaces simple linear stories with circular causation: outputs become future inputs.

When a system helps create the conditions that shape its next state, where should a causal explanation begin?

A good metaphor should eventually make itself less necessary. It gets us close enough to the real system that we can see where the scaffolding ends.

Reading trail

• Aeon — We are not machines
• Aeon — Life as a restless manner of being

These links are starting points for the scientific and historical ideas. The systems interpretation, analogies and conclusions here are my own.