2:00 am philosophy, also known as pub philosophy (although this is closer to 11:00pm), is basically the name for the discussions you have with friends or relatives around this time. Odds are that you will get onto some really unusual topics or problems and suggest "perfect" solutions to them. Unfortunately if you write down your amazing ideas in the morning they will mostly be complete and utter bollocks.
The reason for this is that at this time of night you are probably slightly drunk and over-tired. This combination allows your brain to think in a very lateral fashion but unfortunately ignore any aspects that don't make any sense. It is the same set of feelings and ignored factors that lead to situations such as sleeping with your best friend's girl or running around naked. The only difference is there are still some inhibiters in place and this allows you simply to be really, really deep.
The other definition is that this is what the thoughts which run through your head when you are lying down trying to sleep. These tend to be outrageous plans or ideas that you will never go through with but seem like a really good idea at the time.
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