The numbers of the years have never conveniently tallied with our mental labels of the decades they marked. The "seventies" didn't really begin until 1973, and didn't end until 1983. The "eighties" can first be sighted in 1983, and can still be found in 1993.
But the biggest change between decades - and indeed the real mid-point of the 20th Century - is 1964. The last year of "the fifties" was 1963, and 1964 was to be the first of the "the sixties". The last vestiges of World War Two had been difficult to sweep away, with long years of poverty and austerity breeding a society that was inward looking and rigidly conformist. The new prosperity at the end of the period underlined the stifling nature of this ant-like conformity but failed to break it.
A gunshot in Dallas at the end of 1963 managed it.
1964 saw the world suddenly change. The certainties built up since 1945 were suddenly thrown over as young people began to become politically, socially and economically active. This economic activity, for the first time, turned teenagers and young adults into a market. This new market was awash with money and willing to try almost anything at least once. It had no brand loyalty, so was a level-playing field. And it had few preconceptions.
The BBC was first to make a grab for this market. The existing BBC Television Service was targeted at broadly at middle class, middle-aged people from middle England. Because of the unique and constantly threatened method of funding for the BBC, the Corporation needed to ensure that each generation grew up with the BBC as a constant. This way, major changes or privatisation would be unthinkable like selling a maiden aunt.
The BBC therefore split the Television Service into two networks the 405-line BBC-1 aimed at the original audience, and the 625-line BBC-2 aimed at those willing to experiment and try something new, something hip, something jazzy.
Associated-Rediffusion in London also saw a new market it couldn't quite reach. Although "Ready Steady Go" had set them off in the right direction, the management soon realised that BBC-2 could steal the new market from underneath them by playing a game of hipper-than-thou'.
So Rediffusion London was born, replacing AR's "fifties" brand with a new improved' "sixties" hip and swinging variant.
Both BBC-2 and Rediffusion London (and even RTF2 in France) had to develop a monochromatic identity that would fit in with the new colourful decade. The innovative solution was to replace white-on-black symbols and words with black-on-grey and white-on-grey something almost inconceivable only a few years before.
If you want a pivotal point in 20th Century history, 1964 has it all. A change in fashion, a change in the media, a change in government, a change in market forces, a change in world politics and a change in design rules. You need a world war before you can match it.