What is a cocktail?

What is a cocktail? Let's return to that 1806 definition: 

'a stimulating liquor, composed of spirits of any kind, sugar, water and bitters'

Besides the obvious Old Fashioned and Sazerac, this description most calls to mind Bumbo, the 18th century caribbean pirate's drink of choice. It's made with ingredients that would have been readily available in that part of the world, and so it doesn't seem too great a stretch to imagine that the west indies had a fairly profound influence on the drinking tastes of the time, as the early 19th century recipe for 'cocktail' is very close to this.

Now of course the word 'cocktail' essentially means any mixed alcoholic drink, which is perhaps what leads to some of the apparent confusion over what separates a cocktail from a dirty pint or the combined contents of the average cupboard under the stairs.

This proto-cocktail of the early 19th century has a spirit, a sweetening agent, spices, and a little dilution. What this illustrates is that the cocktail has always been about balance: no haphazard spirit-and-mixer combo this, but something with multiple elements that need to be balanced against one another in order to create something that's more than the sum of its parts. Again, I refer you to Chris McMillian for an illustration of this.

Of course, it's not just Old Fashioneds and sours that require this approach...the same applies equally to a Brandy Alexander, a Martini, or a Bloody Mary. All that differs is the intended overall flavour profile, and the drinker's personal tastes. Whether you're balancing gin against vermouth, or cream against alcohol content, the same basic principles apply in every case.