Tertium quid

For the American political movement, see Tertium Quids.
Electrum, a rare alloy of gold and silver, was used by Tertullian as an example of a tertium quid, by which he meant a mixture with composite properties.

Tertium quid refers to an unidentified third element that is in combination with two known ones.[1] The phrase is associated with alchemy.[1] It is Latin for "third something" (literally, "third what"), a translation of the Greek triton ti (τρίτον τί).[1] The Greek phrase was used by Plato (360 BC),[2] and by Irenæus (c. AD 196).[3] The earliest Latin example is by Tertullian (c. 220), who used the phrase to describe a mixed substance with composite properties such as electrum, a somewhat different sense than the modern meaning.[4]

  1. ^ a b c "Tertium quid", Online Etymological Dictionary
  2. ^ Grote, George, Plato, and the other companions of Sokrates, Volume 2, p. 418. From the dialogue Sophist: "Existence or reality must therefore be a tertium quid, apart from motion and rest, not the sum total of those two items." (250b)
  3. ^ Irenæus, Against Heresies 2.1.3. The surviving text is Latin, but the original would have been in Greek. "But if they say this, there will be a 'tertium quid,' with this immense separation between the Pleroma and what is outside it, and this 'tertium quid' will limit and contain the other two, and will be greater than both the Pleroma and what is outside it, since it contains both in its bosom." (Grant, Robert McQueen, Irenaeus of Lyons, p. 108.)
  4. ^ Tertullian, Adv. Praxean 27. "If, however, it was only a tertium quid, some composite essence formed out of the two substances, like the electrum (which we have mentioned), there would be no distinct proofs apparent of either nature." (That is, of the divine and human natures of Christ.)