If the Equinox is the start of Spring, why is the Solstice the middle of Summer?

We just passed the Spring Equinox, so everyone and their dog is whittering about Spring being finally here. And indeed, the weather is starting to cheer up a bit, although the nights are still around or below freezing here in Toronto (and you know there will be the odd snowfall well into April).

So, if the Spring Equinox is widely considered the start of the Spring season, why is the Summer Solstice not considered the start of Summer? After all, the Summer Solstice is also known as Midsummer (and the Winter Solstice as Midwinter). So, what gives?

Well, it all depends on your definition of Summer, really. If you consider Summer to be the season of long days and short nights, then the Solstice (the longest day of the year, astronomically speaking) is indeed Midsummer. But if you consider Summer to be the season of peak growth and warm weather, then things get a bit murky. 

Weatherwise, Summer here in Southern Canada could be considered to start in mid-May and continue to about mid-September. In the UK - and that's where the word originated, of course - things generally start a little earlier, maybe early May to the end of August (by September things are starting to wind down, and you might consider that month to be part of Autumn). So, on that basis, the latter part of June, when the Summer Solstice falls, could conceivably - at a stretch - be thought of as the middle of Summer (although it's even more of a stretch to think of Spring starting February, even in Britain).

Anyway, the point is, Spring, Summer and the other seasons are not scientifically defined. They are variable, they differ from one country to another, they differ over the centuries, and they are not necessarily a neat three months each in length. So, the words are just convenient labels and should not be taken too literally. Think of them more as a poetical concepts than as products of hard science.