Clarke's Law

Clarke's Law stated that:


 * Any sufficiently advanced form of technology is indistinguishable from magic.

The Captain paraphrased this by describing now-wrecked craft had possessed technologies "indistinguishable from magic." (DW: The Pirate Planet)

The Doctor reminded Ace of Clarke's Law and stated that "the reverse is true", as was the case of the Thirteen Worlds, a parallel universe where technology formed alongside magic. (DW: Battlefield)

Although not referenced specifically, the Sycorax proved Clarke's Law, by thinking of blood control as form of sorcery, due to it giving them power over others. They also accused the Doctor of witchcraft when his hand was able to regrow so soon after his Regeneration cycle. (DW: The Christmas Invasion)

When Angelo Colasanto believed Captain Jack Harkness' Vortex manipulator to be magic, Jack corrected him saying it was technology, although the two could be indistinguishable. (TW: Immortal Sins)