Clarke's Law

Clarke's Law stated that:

Any sufficiently advanced form of technology is indistinguishable from magic.

For example: the Sycorax thought of blood control as form of sorcery as it gave them power over others, they accused the Doctor of witchcraft when he grew another hand. (DW: The Christmas Invasion)

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)

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

Notes

This principle often gets quoted as a singular statement. In fact, Arthur C. Clarke made it the third of three laws concerning predicting the future.