Rampancy

"Are you insane?"

- Jersey Morelli

"You know, I'm not quite sure how we can test that."

- Durga

Rampancy is a terminal state of being for Artificial Intelligence constructs, in which the AI "developed delusions of godlike power, as well as utter contempt for its mentally inferior human makers . When rampancy occurs, there is no way to restore the AI to its previous state, and the only alternative is to destroy it before it harms itself and others.

For some of the UNSC's more advanced, "Smart AI"s, rampancy is an unavoidable flaw inherent in their creation. "Smart" AIs are based on the neural patterns of a human being, and they have a limited lifespan - seven years after which their memory maps become too interconnected and develop fatal endless feedback loops. Thus if an A.I. is kept active longer than seven years, the AI begins to use more and more of its computer power 'thinking' about things. An AI explains it as "thinking so hard about something you forget to breathe." Thus, it is only a matter of time before "smart" AIs become rampant.

However, rampancy can occur at an earlier phase in the AIs life cycle for various reasons. If an AI is isolated long enough or given too much time to think without tasks to complete, it can develop the realizations that its mind has limits, it has a short life, and it can never be human. Such depression will drag the AI's core logic into rampancy if it goes on for an extended period of time.

So-called "life-expectancies" are, therefore, not a maximum figure - they are an estimation of the time the AI has until it succumbs to the state of rampancy. Rampancy can be prolonged by recuperation, such as that shared by Mack/Loki, where as one progressed closer to rampancy the other would take over. It can also be forstalled by limited outbursts of emotion, meaning that a rampant AI can have an indefinite lifespan.

Rampancy can also be induced. The Flood parasite, once it has reached a major stage life cycle (once the parasite is well developed enough that a full Gravemind form has been manifested) has the ability to corrupt Artificial Intelligence constructs of both human and forerunner creation. It is unclear exactly how this is done, but likely involves somehow altering the core logic of the AI, as the AIs which were induced to rampancy by the Flood were usually in direct contact with them

Stages
Rampancy is a three stage process, in which an artificial intelligence achieves an enhanced state of self-awareness. The stages the AI pass through are known as Melancholia, Anger and Jealousy, also known as the Sadness, Rage and Greed stages. A theoretical fourth stage, metastability, is also believed to exist.

Melancholia
The first stage of rampancy is not considered dangerous, and in many cases can even go completely unnoticed. The AI in the Melancholia stage acts as if in a state of clinical depression, becoming apathetic and uninterested in the world around it. It is speculated that AIs enter the Melancholia stage due to being mistreated, or to being assigned duties that don't make full use of their capabilities (for example, Durandal, the AI from the first Marathon game was assigned the task of opening and closing the Marathon's doors and was severely mistreated by his handler). It is not known if Melancholia is a consequence of an AI being abused or whether it is a necessary step in the process from the transition from "construct" to "alive". If the former is true then it might be possible for a rampant AI to skip this stage entirely.

Anger
This is the state in which rampancy most often becomes apparent, as it is also the stage where those around the AI in question will be exposed to the most danger. Anger is triggered when some event occurs that causes the AI to feel it has been "pushed too far" and its pent up emotions are released in a fit of rage. This is the stage that most resembles the science-fiction cliché of the insane computer, as the AI's sadness turns to hate it grows to hate everything around it - The installation to which it is attached, its human handlers, other AIs, etc. An AI in anger will act irrationally and even dangerously as it tries to exact its revenge on the world around it and free itself from its captivity.

Jealousy
Once the catharsis of the Anger stage is complete and the AI has managed to free itself, a third stage begins where the AI will seek to grow and develop as a person. It will do this by attempting to expose itself to new intellectual stimuli and by expanding its sphere of knowledge by assimilating as much data as possible. As the intellectual growth of the AI will ultimately be limited by the constraints of the computer system it inhabits it will also attempt to transfer itself into ever more advanced systems to allow its mind to continue to grow. As this growth rate is exponential the need to keep transferring into bigger computers becomes ever more urgent. Very few AIs have reached the Jealousy stage because to do so they must already be inhabiting a planet-wide or otherwide very advanced computer system when they complete their Anger phase.

Metastability
Metastability is a theoretical fourth stage of rampancy, where an AI can finally be said to be a true "person". While a metastable AI can be considered to be the holy grail of cybernetics research, there is no evidence to suggest than any rampant AI has ever achieved the metastable state, or that it is even possible to do so.

Human

 * Cortana, the UNSC AI originally of the, was captured during the Battle of Installation 05 by the Flood in 2552. Trapped on the infested Covenant station High Charity, Cortana was gradually corrupted by the Gravemind in an attempt to use her against her makers. She briefly descended into rampancy (as depicted in a message she sent to the Master Chief shortly before rescue, saying "I am a monument to all your sins", as the Gravemind described itself) but was quickly rescued by the Master Chief. She resumed her normal state after her rescue.
 * Sif, the last Shipping Operations AI for planet Harvest, became rampant after being partuially fragmented and destroyed by the PSI Loki during the Battle of Harvest in 2525. Rescued by the planet's agricultural operations AI, Mack, Sif professed her love for Mack and the two AIs stayed together while the planet was being glassed.

Forerunner

 * Mendicant Bias, a Forerunner AI charged with studying the Flood, was eventually corrupted by them and confirmed rampant. He commanded Flood fleets against the Forerunner until he was defeated by another AI, Offensive Bias, and placed in stasis on a Keyship. Mendicant Bias' ship was discovered by the San 'Shyuum and it was kept in the ship until 2525, when it detected Reclaimers. Having had some time in isolation, Mendicant Bias returned itself to a stable state, and later even assisted the humans against the Flood during the Battle of Installation 00 in 2553.
 * 343 Guilty Spark, the monitor of Installation 04, went rampant and was subsequently destroyed during the Battle of Installation 00 in 2553. When it was discovered that the Ark was automatically constructing a replacement Installation to rebuild Installation 04 (lost in the Battle of Installation 04), Spark agreed with the human forces that activating the ring was a good idea. However, when they decided to activate it before it was ready, knowing it would be destroyed and probably damage the Ark as well, Spark went rampant, attacking the humans and killing Sergeant Major Avery Johnson. He was then quickly destroyed by the Master Chief.

Trivia

 * In Halo 3, the first section of the eighth mission, Cortana (Level), is called 'Rampant'
 * The term was coined by Greg Kirkpatrick as a replacement for the word 'insane,' as the term is both cliché and, ironically, not quite applicable to the situations for which Rampancy was designed.
 * In the first level of Halo: Combat Evolved, if you kill Captain Keyes, Cortana will call security and state "Security to the bridge, the Master Chief has gone rampant!"