Summer officially began just a few days ago—at least that’s what the calendar says. June 20 was the summer solstice, the day when the northern hemisphere is most inclined towards the sun and consequently receives the most daylight. By this definition, summer lasts until the autumnal equinox, in late September, when days and nights are of equal length. But by other definitions, summer starts at the beginning of June and goes through August. Other less formal definitions may put the start of summer on Memorial Day or after the end of the school year (which for my children were the same this year).
For years I wondered why summer officially began so late into June. After all, shouldn’t the solstice, as the day when we receive the most sunlight, be the middle of summer rather than the start? But even though it receives the most sunlight, it’s not the hottest, thanks to something called seasonal lag. The oceans absorb a large amount of heat and continue to release that heat for quite some time after the solstice, so the hottest day may come a month or more after the day that receives the most solar energy. Summer officially starts later than it should to compensate for this lag.
But what does this have to do with language? It’s all about definitions, and definitions are arbitrary things. Laypeople may think of June 1 as the start of summer, but June 1 is a day of absolutely no meteorological or astronomical significance. So someone decided that the solstice would be the official start of summer, even though the period from June 20/21 to September 22/23 doesn’t completely encompass the hottest days of the year (at least not in most of the United States).
Sometimes the clash between common and scientific definitions engenders endless debate. Take the well-known argument about whether tomatoes are fruit. By the common culinary definition, tomatoes are vegetables, because they are used mostly in savory or salty dishes. Botanically, though, they’re fruit, because they’re formed from a plant’s ovaries and contain seeds. But tomatoes aren’t the only culinary vegetables that are botanical fruits: cucumbers, squashes, peas, beans, avocados, eggplants, and many other things commonly thought of as vegetables are actually fruits.
The question of whether a tomato is a fruit or a vegetable may have entered popular mythology following a Supreme Court case in 1893 that answered the question of whether imported tomatoes should be taxed as vegetables. The Supreme Court ruled that the law was written with the common definition in mind, so tomatoes got taxed, and people are still arguing about it over a century later.
Sometimes these definitional clashes even lead to strong emotions. Consider how many people got upset when the International Astronomical Union decided that Pluto wasn’t really a planet. People who probably hadn’t thought about planetary astronomy since elementary school passionately proclaimed that Pluto was always their favorite planet. Even some astronomers declared, “Pluto’s dead.” But nothing actually happened to Pluto, just to our definition of planet. Astronomers had discovered several other Pluto-like objects and suspect that there may be a hundred or more such objects in the outer reaches of the solar system.
Does it really make sense to call all of these objects planets? Should we expect students to learn the names of Eris, Sedna, Quaoar, Orcus, and whatever other bodies are discovered and named? Or is it perhaps more reasonable to use some agreed-upon criteria and draw a clear line between planets and other objects? After all, that’s part of what scientists do: try to increase our understanding of the natural world by describing features of and discovering relationships among different things. Sometimes the definitions are arbitrary, but they’re arbitrary in ways that are useful to scientists.
And this is the crux of the matter: sometimes definitions that are useful to scientists aren’t that useful to laypeople, just as common definitions aren’t always useful to scientists. These definitions are used by different people for different purposes, and so they continue to exist side by side. Scientific definitions have their place, but they’re not automatically or inherently more correct than common definitions. And there’s nothing wrong with this. After all, tomatoes may be fruit, but I don’t want them in my fruit salad.