Dammit, I had this argument back in March.
Wikipedia sums it up best for me:
"But, because the seasonal lag is less than 2/20 of a year (except near large bodies of water), the meteorological start of the season, which is based on average temperature patterns, precedes by about three weeks the start of the astronomical season. According to meteorology, summer is the whole months of December, January, and February in the Southern Hemisphere, and the whole months of June, July, and August in the Northern Hemisphere. This meteorological definition of summer also aligns with commonly viewed notion of summer as the season with the longest (and warmest) days of the year, in which the daylight predominates, through varying degrees. The use of astronomical beginning of the seasons means that spring and summer have an almost equal pattern of the length of the days, with spring lengthening from the equinox to the solstice and summer shortening from the solstice to the equinox, while meteorological summer encompasses the build up to the longest day and decline thereafter, so that summer has many more hours of daylight than spring."
http://en.wikipedia.org/wiki/Summer
Which is to say: Summer is weather for me, not astronomy. It might've been astronomy. But so was trigonometry once upon a time. Similarly with geometry on land. If I want to measure the angle of something I don't need to be trying to work out who owns what land after the Nile has flooded.
I'm happy with wholey June, July, August being my summer months. Similarly, December 1st can happily be in Winter.
[hr]
"There is only ever one truth. Things are always black or white, there's no such thing as a shade of grey. If you think that something is a shade of grey it simply means that you don't fully understand the situation. The truth is narrow and the path of the pursuit of truth is similarly narrow."
Also, some years later:
"here we are arguing about a few uppity troublemakers with a bee in their bonnet and a conspiracy theory."