Synchronicity was, according to the Third Doctor, "the principle that a coincidence may happen without any causal link and yet still be significant". He made this observation in relation to the fact that the Brigadier and Sarah happened to be in Sicily simultaneously. The Doctor went on to say that many schools of philosophy were based upon synchronicity. When the Brigadier suggested that synchronicity was essentially the notion of pre-destination, the Doctor basically agreed, saying that fatalism was a cruder expression of the same idea. (AUDIO: The Ghosts of N-Space)