A letter to the household hints columnist “Heloise” provides a paradigm for the way our knowledge of the world alters over time. A reader writes to say that of course everyone knows that putting some lemon juice or citrus on fresh-cut fruit keeps it from turning brown and enhances the taste. For those who may find themselves momentarily without a lemon or lime, however, she recommends using powdered lemonade mix, which has the same effect.

This is a good example of lateral thinking: if a lemonade isn’t available, try using lemonade mix. The problem is, someone trying this out might discover it doesn’t work. I’m not convinced, as it is, that powdered “lemonade” mix has much to do with lemons. It seems likely to me it’s nothing but chemicals. In fact, one of them may be an acid that produces the tartness of chemical lemonade, but I’d guess that it’s not the same acid that’s in lemons—assuming that’s what produces the brown discoloration of cut fruit.

Putting ourself in the position of the person in the kitchen who’s been told that lemons prevent cut fruit from turning brown, we can see the logic of moving from lemons to lemonade mix. It might or might not work, as someone wise to the ways of the mass-market food preparation world would be aware, since many things which bear the names of natural products have nothing to do with those products. If all we need to know is that lemons produce the effect we want, that’s what we know: lemons produce this effect. It’s only if we have to substitute something for lemons, lemons (say) being unavailable, or if something goes wrong that we look for an “explanation” of what causes lemons to have this effect. We don’t ask for a more precise “explanation” than the explanation we already have unless the one we have fails to work or must in some way be generalized.

Because the properties of citrus fruit is not virgin territory, it seems likely that the active ingredient is an acid of some sort, this being the most remarkable quality of lemons. It probably suffices to ask someone with a degree in nutrition to get the answer. An educated guess would suggest that there is some acid in powdered lemonade that produces the same result, though not necessarily the same one as what we call citric acid in lemons. Something produces the “tang” in powdered lemonade. If we isolate this, we can ask what other sources contain it. Perhaps it’s not powdered lemonade at all, but other household items or prepared foods. We can suggest other things that seem to belong to this same family—though in fact for our purposes they may not. Perhaps vinegar has the same result—though we would understand that taste issues would be the reason why this is not generally suggested as an alternative. But perhaps a splash, with lots of sugar, in an emergency…

In any questioning situation, there is a layer of what we have and the layer of “explanation” we are looking for in order to bring the world into focus. The explanation is an explanation with respect to the layer we have; it itself might require its own explanation some day. For someone with an unlimited supply of lemons, knowing that “lemons prevent fruit from turning brown” may itself be the explanation, the response to a child that asks, “Grandma, why are you squeezing lemons on the peaches?” “Lemons” in general and “fruit” in general are already explanations with respect to these lemons, these peaches.

In simple cases like this, it’s likely we already collectively have the answers to questions like, what is it in lemons that keeps peaches, or any fruit, from turning brown (not all fruit turns brown, so this too is something we might want explained: which fruit turns brown and why?). We have only to ask.

It’s not absolutely necessary that we find ourselves without lemons before we ask this question, though this is likely to be the impetus. It’s perfectly possible that someone idly wondering might ask, Is there anything else that can have this effect? This is the mind-set of what we call “pure science”; people who set about looking for explanations for things we don’t have an immediate need for. But later on, suddenly, people might well need this explanation, say if the lemon supply dries up.

The explanations we come up with are always the generic ones of the order of “lemons cause fruit to stay fresh.” They are generic by contrast with subsequent explanations. The explanation we come up with always seems more specific, seems to fit exactly the hole we want to fill. Only it’s always possible that this itself will have to be refined; what seemed a perfect fit no longer is a perfect fit.

Now we say, it’s not lemons that cause this effect, it’s the acid in the lemons (i.e. not the rind, not the color, not the shape, not even the fact of its being a fruit). We’ve refined our statement. Science is the process of helping us get to the more refined statement, not the statement itself. When we had lemons, saying that “lemons” cause this effect was satisfactory: to us it seemed as if this explanation filled the hole we had. There’s no guarantee that circumstances will continue to leave us satisfied with a statement, however. We can be satisfied by saying that “acid” or “acid X” causes this effect. But perhaps the day will come when the fruit fails to be kept from browning when we apply what we take to be another source of this acid, or a pure form from the laboratory. At that point we may realize it wasn’t the acid itself, it was some property of the acid, or this acid in these circumstances.