In Abhidharma, there are forty-six factors grouped into six categories of omnipresent factors 大地法 (10), wholesome functions 大善地法 (10), major afflictions 大煩惱地法 (6), major unwholesome functions 大不善地法 (2), minor afflictions 小煩惱地法 (10), and indeterminate functions 不定地法 (8)

In the Yogâcāra 唯識 system, there are fifty-one mental functions, which are divided into six groups:

1. five omnipresent functions 五遍行;
2. five object-contingent functions 五別境;
3. eleven wholesome functions 十一善;
4. six primary afflictions 六煩惱;
5. twenty derivative afflictions 隨煩惱, and
6. four indeterminate functions 四不定 (indeterminate in terms of wholesome/unwholesome, contingency of object, and liminality and subliminality).

According to Sarvâstivāda 有部Abhidharma teaching, the mind 心王 and its concomitant factors mutually cause one another through the mechanism of simultaneous causation 倶有因 (sahabhūhetu), and in particular, a subset of simultaneous causation known as mutually conjoined causation 相應因 (saṃprayuktakahetu) 〔順正理論 T 1562.29.417c20〕 . The mind and its concomitant factors have each other as mutual causes and share the common effect [同一果倶有因] of cognizing the same object 同一所緣. According to the Cheng weishi lun, the mind grasps the general characteristic 總相 of the object, while the factors concomitant with the mind also grasp the specific characteristic 別相 of the object 〔成唯識論 T 1585.31.26c17〕 . *Mahāvibhāṣā likens the mind to a merchant and the concomitant mental factors to the 'companions' 伴侶 the merchant remains inseparable with while crossing a treacherous path of road frequented by brigands 〔阿毘達磨大毘婆沙論 T 1545.27.80c29〕 According to Sarvâstivāda teaching, mind and its concomitant factors evince five aspects of equivalence (pañca samatāprakāra 五義平等) when they arise together:

1. The two are equivalent in their underlying sensory faculty 所依平等
2. The two are equivalent in their percept 所緣平等
3. The two are equivalent in their mode of activity 行相平等
4. The two are equivalent in the time they discharge causal efficacy時平等
5. The two are equivalent in their object 事平等

There are ten universally operating mental factors 十大地法 in Sarvâstivāda taxonomy which are invariably present in each moment of mental activity. For epistemological tenets surrounding the relationship between the mind and factors concomitant with the mind in Abhidharma teaching, see Dhammajoti (2004, chapter 6, “Epistemological Tenets Surrounding Thought and Thought Concomitants”). Mochizuki (vol. 3, 2066d-2067a) provides a detailed account of the various taxonomies of factors concomitant with mind found in Abhidharma and Yogācāra literature. For a related discussion in the Sarvâstivāda system, see 心隨轉法.

References:

Dhammajoti, K. L. 2007. Abhidharma Doctrines and Controversies on Perception (3rd revised and enlarged edition). Hong Kong:  Centre of Buddhist Studies, HKU..