Mental Model Fallacy (2018)
The usage of the term &quot;mental model&quot; here seems <i>really weird</i> to me.<p>Once upon a time, a &quot;mental model&quot; was, in particular, a <i>model</i>: some sort of mental representation of a thing, usually simpler and clearer than the thing itself.<p>I&#x27;ll give some concrete-ish examples.<p>- For anyone you know reasonably well, you can probably make a lot of predictions about how they would react to various things. Whatever you use to do that -- which may well be fuzzy and complicated and largely inaccessible to you -- is your mental model of that person.<p>- Sometimes you might explicitly model someone as a &quot;homo economicus&quot; money-maximizer, who will always do whatever gets them the most money. This is obviously an extreme simplification, but it has the merit of being something you can explicitly reason about.<p>- Your mental model of the US government might be that the president makes decisions and everyone else does exactly what he says. This would be a <i>hopelessly wrong</i> model, of course.<p>- If you&#x27;re good with differential equations, your mental model of a pandemic might be something like the Kermack-McKendrick SIR model, and that might give you useful intuitions for the consequences of (e.g.) implementing social-distancing measures.<p>- If you&#x27;re not so good with differential equations, you might adopt a simpler model that just says that the number of infections is an exponential function of time. Even that&#x27;s enough to make better decisions than many people do.<p>But here &quot;mental model&quot; seems to be being used to be generalized way beyond that, to include any <i>way of thinking</i> or <i>broadly applicable idea</i>. A few examples from the Farnam Street list linked near the start of the article: &quot;First principles thinking&quot;, &quot;Thought experiment&quot;, &quot;Second-order thinking&quot;, &quot;Inversion&quot;, &quot;Occam&#x27;s Razor&quot;. Some of these are useful tools when building mental models. Some of them are useful things to do, or keep in mind, whatever sort of thinking you&#x27;re doing. None of them is a <i>model</i>.<p>In fact, almost <i>nothing</i> in the Farnam Street list is a model. But some of the things in the list are <i>useful metaphors</i>, which you could consider to be tiny models, or model-parts. (For instance: &quot;velocity&quot;. Velocity is not a mental model, but you might often want to build mental models that include something you could reasonably call &quot;velocity&quot;.)<p>Is the usage of &quot;mental model&quot; to mean &quot;any thinking tool at all&quot; actually widespread? I&#x27;ve seen it before, but I think the other instances I&#x27;ve seen have been closely linked with this one -- all, I think, quoting Charlie Munger. (I don&#x27;t know whether Munger&#x27;s own use of the term is as broad as e.g. Farnam Street&#x27;s.)<p>I hope it isn&#x27;t; the narrower notion in which a mental model is actually a <i>model</i> seems to me a valuable one, and it seems easier to find other terms that convey the broader idea (e.g., &quot;thinking tool&quot;, &quot;general principle&quot;, &quot;idea&quot;) than good replacements for the narrower one.