Congruent-Enigmatic scale

Enigmatics is a Covenant (originally Forerunner) classification describing sapient beings which diverge considerably from the cognitive and physiological baseline defined by the Covenant's ruling species. It is analogous to, though more specific than, the human scientific concepts of xenosophonts and even the hypothetical category of cryptosapients.

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, 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.

In contrast, Enigmatics are species which, while demonstrably intelligent, sharply deviate from one or more of these commonalities. 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".

List of known Enigmatic species

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