Congruent-Enigmatic scale

The Congruent-Enigmatic scale is a Covenant classification system used to describe various types of sapience. In simple terms, the scale runs from "familiar" to "alien", from the standpoint of the San'Shyuum and the Sangheili.

Species like humans, San'Shyuum, Sangheili, Unggoy, Jiralhanae and Kig-Yar occupy a relatively narrow portion of the spectrum of sapient life. All are bilaterally symmetrical, upright, four-limbed, and have a roughly analogous capacity for object manipulation. While their exact cognitive processes and median levels of intelligence vary, these differences do not pose considerable obstacles to everyday interaction. All possess fully-independent and self-contained consciousnesses and have the mental capacity to grasp most of the same basic concepts and to share similar values, even if they do not always do so. Likewise, all use vocal utterances as their primary means of communication and are capable of speaking the same languages, even if imperfectly at times. To the Covenant, these are known as Congruent species. The closest to this is the human concept of anthroposapience, or "human-like" sapience, with aliens who fit that criteria being classified as xenoanthrophonts, i.e. aliens who are loosely humanoid in their psychology and body plan. The exact definition of just how close alien intelligence has to be to humanity to qualify as "anthropomorphic" is disputed and varies, however. Generally, these are beings who experienced broadly similar evolutionary pressures as Homo sapiens and developed on relatively similar worlds. No such being is psychologically identical to humans, but the mental and physiological gap is not too overwhelming for meaningful correspondence to occur.

In contrast, Enigmatics are species which, while demonstrably intelligent, sharply deviate from one or more of these cognitive and physiological commonalities. It is analogous to, though more specific than, the human scientific concepts of xenosophonts and cryptosophonts. The former are defined as sapients that defy or redefine the human concept of sapience, while the latter are hypothetical sapient entities so alien we are unable to tell they are in fact sapient. They may occupy a native biome that largely excludes them from everyday interaction, such as the Xar-Shaa. They may think much faster or slower than most other species, or in ways so different from other species that make interaction with them a challenge. Some may be entirely incapable of grasping concepts many species regard as the building blocks of civilization, such as language, religion or technology. Others exhibit clearly alien forms of cognition, such as eusocial hive-minds (e.g. the Yanme'e) or colonial gestalt intelligences (e.g. the Lekgolo). However, there is no universally agreed-upon line between Congruent and Enigmatic. As the old adage regarding sapience goes, "It's hard to define it, but you know it when you see it".

The scale
The following lists species in descending order from Congruent to Enigmatic, as recorded by the chronicler Nor Khebka in 2563. In some cases, it is difficult to truly pinpoint the specific order in which species should be listed, and it should be noted that any such ranking is subject to the author's biases. For example, the few lists that did include humans during the Human-Covenant War would list humanity much further down the list than later, more sympathetic interpretations.


 * Congruents
 * San'Shyuum
 * Sangheili
 * Kig-Yar
 * Human
 * Jiralhanae
 * Unggoy
 * Cix-Tu
 * Ior
 * Rhiln
 * Sharquoi


 * Enigmatics
 * Huragok
 * Yanme'e
 * Lekgolo
 * Chelukhi
 * Xar-Shaa

The Flood theoretically represents the ultimate enigmatic organism as their goals and the very nature of their existence are fundamentally antithetical to the continued existence of all other life. However, the Flood (or Parasite) is typically excluded from Covenant species taxonomies because they are regarded as a metaphysical entity, an elemental manifestation of chaos and corruption, rather than a form of life in the traditional sense.