> Jevons paradox happens when the cost of a resource goes down, but the total spend on that resource goes up.

I would argue that is not Jevons paradox but standard supply and demand (and this "reverse Jevons paradox" too). Jevons paradox occurs when a more efficient use of a resource leads to an increase in its use (instead of a decrease as a first order analysis would suggest).

Supply and demand says when something is cheaper (or produced more efficiently), people will use more of it. But the critical part is that it doesn't say people will spend more on it.

Jevon's paradox is a special case of supply and demand, where people actually end up spending more money because something is cheaper.

It's interesting because consumption then grows in unpredictable ways: it can drive innovation even in cases where markets are constrained by monopolies, for example, where in non-Jevons cases producers would have no incentive to lower prices.

> Jevons paradox occurs when a more efficient use of a resource leads to an increase in its use

I think these are the same, because efficiency is value over cost. In the original formulation of the paradox, a more efficient steam engine lead to a rise in coal consumption. You can look at this as a "money buys coal, coal drives locomotion" system, where the latter part was improved. Modulo practical issues with coal (transport, storage, etc), dropping the price of coal would (probably?) lead to the same effect, since the end result is that locomotion per money is increased. For an outside observer, it doesn't matter if you get more coal per money or more locomotion per coal.

> standard supply and demand

Standard supply and demand doesn't say anything about increase of spend. If food prices drop, I'm not going to buy more food. I might buy better food for the same budget, but there's no reason why my total food spend should increase.

> I would argue that is not Jevons paradox but standard supply and demand (and this "reverse Jevons paradox" too).

Kinda yes. How do you derive total spend from supply-demand curves? Multiply price and quantity at an intersection point. Likewise, you can predict total spend by multiplying p and q on the demand curve.

The difference in total spend is difference between these areas. For the total spend to increase with a drop in price, the the demand must rise faster.

Jevon's paradox implies that the price equilibrium is at the highly elastic portion of the demand curve.

> Jevons paradox occurs when a more efficient use of a resource leads to an increase in its use

While that's mostly true in practical reality in established economies, that does not strictly have to be the case. On the consumer side, especially in manufacturing, there's very little difference between unit price of a good falling and input unit per output units dropping as both lead to decreased COGS. In both cases, market realities might unlock alternative approaches (the classic being robot replacing Robert), leading to increased demand.

I think it's still valid to see this as an example of the Jevons paradox: Your resource is money, and reduced per-unit cost means you are using your money (resource) more efficiently. If the total spend now goes up instead of stagnating or decreasing, you've got Jevons

you are absolutely correct, the author is putting the cart before the horse.