Machine Spirit

In the fictional universe of Warhammer 40,000, a Machine Spirit is a spirit believed by the Adeptus Mechanicus (and, from that source, by most other humans from the Imperium of Man) to inhabit and control a piece of machinery. The functioning, or lack thereof, of any machine is believed to be the result of its spirit's disposition. To keep their machine spirits happy and cooperative, operators therefore make numerous ritualised advances to their machinery. These depend on the machine, but in most cases include various maintenance rituals and prayers of function and occasionally also an offering or libation. The more so if the machine is large or important. Machine spirits are believed to be bestowed by the Machine God and subservient to him.

Because alien technologies do not make observances to their machine spirits, many among the Adeptus Mechanicus see them as grave heresies that must be destroyed rather than studied, even if superior to human-manufactured counterparts in operation. This view is not universal, however. Indeed, many human colonies near the boundaries of the Tau Empire were found to be using Tau technology for agricultural purposes during the Damocles Gulf Crusade, and the offending colonists were punished with penal sentences.

Artificial intelligence (or Abominable Intelligence, as it is known in the Imperium) is generally prohibited in the Imperium unless a human is combined with it or part of its circuitry. This is to ensure the intelligent machine does not rebel against its human masters. However, some machines are allowed such an intelligence under the guise of having an especially active machine spirit. An example of this is the Land Raider tank, which can continue to move and fire, albeit with a lesser ability, even if its crew is unable to fight. In the Relic Entertainment RTS game Warhammer 40,000: Dawn of War the Space Marine Land Raider unit has a special ability that allows its machine spirit to take control of the Land Raider. As such the tank moves and fires much more slowly, but its ability to absorb damage is increased. Titans have particularly complex machine spirits and can exhibit personalities of their own.

According to the theory wherein the Machine God is actually the C'tan known as the Void Dragon, the machine spirit could be instead a piece of Necron technology, alien to such a point that is it not to be considered conventional AI, and integrated with the Imperium's technology to the point where all human-based technology is now inoperable without one. This would explain why imperial technology does not work without a machine spirit, and why alien and pre-imperial technology can function without a spirit.