Citta differ by sampayutta-dhamma that are "hetu".

 The reality that is sankhara-dhamma cannot arise spontaneously by itself without any paccaya.  There are 3 paramattha-dhamma that are sankhara-dhamma, namely citta, cetasika and rupa.  Citta arises from cetasika as paccaya and some citta arise from cetasika and rupa as paccaya. Rupa arises from rupa as paccaya and some rupa issue from citta, cetasika and rupa as paccaya.  Thus citta differ by hetu: some citta arise concurrently with cetasika that are hetu and some with cetasika that are not hetu.

 The paramattha-dhamma that are hetu consist of only 6 cetasika comprising

 1. Lobha-cetasika as lobha-hetu.  -
 2.  Dosa-cetasika as dosa-hetu.               - 3 akusala-hetu altogether.
 3.  Moha-cetasika as moha-hetu.  _
 4.  Alobha-cetasika as alobha-hetu.  -
 2.  Adosa-cetasika as adosa-hetu.           - 3 sobhana-hetu altogether.
 3.  Amoha-cetasika as amoha-hetu.  -

 The reality that is abyakata-dhamma is one that is neither kusala nor akusala.  Therefore the vipaka-citta, kiriya-citta, vipaka-cetasika, kiriya-cetasika, rupa and nibbana are abyakata-dhamma because they are neither kusala nor akusala.

 The six hetu are categorized as 2 kinds
 The 3 akusala-hetu, namely  lobha-cetasika, dosa-cetasika and moha-cetasika.
 The 3 sobhana-hetu, namely alobha-cetasika, adosa-cetasika and panna-cetasika.

 The four paramattha-dhamma, or citta, cetasika, rupa and nibbana classified by hetu:

Citta           is not hetu.
Cetasika   of which only 6 are hetu, all others (46 cetasika) are not hetu.
Rupa          is not hetu.
Nibbana    is not hetu.

 The dhamma that are not hetu are called nahetu in Pali.  Therefore all dhamma can be classified into 2 categories: hetu and nahetu.

 The 6 cetasika are hetu.  Citta, rupa and nibbana and the other 46 cetasika are nahetu.

 The citta and 46 other cetasika are nahetu or not hetu.  But there are some citta and cetasika that arise concurrently with the 6 cetasika that are hetu while other citta and cetasika do not arise with cetasika that are hetu.  The citta and cetasika that do not arise concurrently with the 6 cetasika that are hetu are ahetuka-citta and ahetuka-cetasika.  Any citta and cetasika that arise concurrently with the cetasika that are hetu are sahetuka-citta and sahetuka-cetasika.

 The cakkhu-vinnana-citta that is seeing objects that appear arise only with 7 cetasika, namely phassa-cetasika, which performs the function of coming into contact with the rupa in contact with the cakkhu-pasada; vedana-cetasika, which performs the function of indifference as upekkha-vedana (adukkhamasukha); sanna-cetasika, performs the function of remembering ruparammana; cetana-cetasika, performs the function of intent, volition, endeavoring, prompting the citta and cetasika arising with it to complete a task; jivitindriya-cetasika, performs the function of supporting and maintaining the concurring dhamma, or citta and cetasika, in the thiti-khana; ekaggata-cetasika, performs the function of focussing on the arammana appearing; and manasikara-cetasika, performs the function of attending to the ruparammana.  These 7 cetasika are not the 6 cetasika that are hetu, therefore, cakkhu-vinnana-citta is an ahetuka-citta.  The lobha-mula-citta that arises in sequence to that cakkhu-vinnana has 2 hetu-cetasika arising concurrently.  They are lobha-cetasika, the reality that is pleased with the object appearing and moha-mula-citta arising concurrently. Lobha-mula-citta is therefore sahetuka-citta.

 Dhamma are separable into 2 categories by hetu, being hetu and nahetu, sahetuka and ahetuka, as follows.

Nibbana and rupa are nahetu and ahetuka.
Citta are nahetu, some are sahetuka and others are ahetuka.
The 46 cetasika are nahetu, some are sahetuka and others are ahetuka.
The 6 cetasika, namely lobha-cetasika, dosa-cetasika, moha-cetasika, alobha-cetasika, adosa-cetasika and panna-cetasika are hetu and sahetuka except for moha-cetasika arising with moha-mula-citta because moha-cetasika arising with moha-mula-citta are ahetuka.

Likewise, dosa-cetasika is also sahetuka.

Moha-cetasika that arises with lobha-cetasika in lobha-mula-citta is sahetuka because there is lobha-cetasika, which is a hetu, arising concurrently.

Moha-cetasika that arises with dosa-cetasika in dosa-mula-citta is sahetuka because there is dosa-cetasika, which is a hetu, arising concurrently.

Moha-cetasika that arises with moha-mula-citta is ahetuka because there are no lobha-cetasika or dosa-cetasika arising with it.
 

Phassa-cetasika is a nahetu but it arises with all citta.  If a citta arises with one of the 6 cetasika that are hetu, then the phassa-cetasika would be sahetuka. If any citta is ahetuka, or without the 6 cetasika that are hetu arising concurrently, then the phassa-cetasika that arises with it would also be ahetuka.  Therefore, phassa-cetasika are nahetu, sometimes sahetuka and others ahetuka.

In each person's daily life there must be both sahetuka- and ahetuka-citta.  But since one hadn't heard the dhamma, one would not know which instant is sahetuka- or ahetuka-citta.  The Buddha had manifested the characteristics of citta in great detail, which instant of citta is ahetuka-citta, which sahetuka-citta and whether the citta that is sahetuka-citta arose with hetu, if so, how many hetu, and how many cetasika arose concurrently with it.

Moha-mula-citta has only one hetu arising with it, therefore it is eka-hetuka (single cause).

Lobha-mula-citta arises with two hetu: moha-hetu and lobha-hetu, therefore it is davi-hetuka (double cause).

Dosa-mula-citta arises with two hetu: moha-hetu and dosa-hetu, therefore it is davi-hetuka (double cause).

As for kusala-citta there must be sobhana-hetu arising with it, otherwise it cannot be kusala-citta.  There are 2 kinds of kusala-citta: kusala-citta that does not arise with panna-cetasika and kusala-citta that arises with panna-cetasika.  Therefore kusala-citta that does not arise with panna-cetasika would have  2 cetasika that are hetu arising concurrently.  These are alobha-hetu and adosa-hetu.  Therefore the citta is davi-hetuka.  The kusala-citta that arises with panna would have 3 cetasika that are hetu arising with it: alobha-hetu, adosa-hetu and amoha-hetu.  Therefore it is ti-hetuka (triple cause).  Kusala-citta is never eka-hetuka because there must be both alobha-cetasika and adosa-cetasika arising concurrently for it to become kusala-citta.
 

How are the terms hetu and paccaya different?

 Paccaya is a reality that benefits and assists other realities to arise or maintain them according to the specific kinds of conditions such as phassa-cetasika, which is not a lobha-cetasika, while both phassa-cetasika and lobha-cetasika are paccaya beneficent to the  arising of other realities such as citta, cetasika and rupa since the characteristics and functions of phassa-cetasika differ from those of lobha-cetasika, the phassa-cetasika would be a different paccaya from lobha-cetasika.

 Phassa-cetasika is condition by being an ahara-paccaya. Ahara is a reality that brings results but it is not so steadfast as to make things flourish like the main root of a tree.  While the realities that are hetu are paccaya by becoming the causes, like the tap root.  Trees cannot flourish with the tap roots alone.  There must be soil and water as nutrients.  But without this main root, the soil and water cannot make the tree develop fully.  Trees with tap roots would flourish differently from plants without one in the same way.  Other realities than the 6 cetasika that are hetu are paccaya by being other conditions and not hetu-paccaya.

 The Patthana Book, which is the seventh and last book in the Abhidammapitaka, manifests realities by their inter-conditioning: by being different paccaya.  The first paccaya is hetu-paccaya, which shows the importance of realities that are hetu.  At funerals when bhikkhu intone the abhidamma, they begin with "hetu-paccayo", which are lobha-hetu, dosa-hetu, mohahetu, alobha-hetu, adosa-hetu and amoha-hetu, to remind us that the realities that are causes for future results as future lifetimes and beings, are the six cetasika, namely lobha-cetasika, dosa-cetasika, moha-cetasika, alobha-cetasika, adosa-cetasika and panna-cetasika.

 Truly, each kind of reality is of its own specific importance.  The Buddha not only manifested one but many paccaya.  Nor did he merely manifest arammana that is paccaya for citta to arise and experience it (the arammana) as the only "arammana paccaya" for the citta.  But he manifested each and every paccaya in detail for the 24 major paccaya as well as their minor paccaya.

 Cakkhuppasada-rupa arises because of other paccaya than the hetu-paccaya.  And cakkhuppasada is, in turn, a paccaya by being the reality that is eminent: the indriya-paccaya, or being paccaya by being a reality that is predominant in its duty and function.  Cakkhuppasada is cakkhundriya, the rupa which is the principal in being paccaya for cakkhu-vinnana to arise and see visual objects through the eyes.  Without cakkhuppasada, sotappasada, ghanappasada, jivhappasada and kayappasada, what would this body be like?  Like a log that does not see, hear, smell, taste or know bodysense contact.  Therefore, the 5 pasada-rupa are paccaya by being indriya-paccaya or eminent in their specific functions such as the cakkhuppasada-rupa being predominant in coming into contact with ruparammana thus causing cakkhu-vinnana to arise and see what appears through the eyes because other rupa cannot perform this function.  The object appearing through the eyes could be clear or not depending on the state, the clarity of the cakkhuppasada-rupa, which does not depend on cetana or desire or intention of anyone but on the indriya-paccaya of seeing, namely the cakkhuppasada-rupa.

 All realities are paccaya for other realities to arise by being diverse kinds of paccaya.  Lobha-cetasika, dosa-cetasika, moha-cetasika, alobha-cetasika, adosa-cetasika and panna-cetasika are paccaya by being hetu.  Each day there are many akusala-hetu arising and some kusala-hetu, but when compared proportionately, kusala-hetu are much less frequent.

 When will kusala-hetu slowly develop until it is stronger than the akusala kind?  One must develop panna to know the characteristics of realities as they truly are because knowing characteristics of realities as they truly are is panna-cetasika, which is amoha-hetu.  As long as panna has not fully realized the characteristics of realities as they truly are, it is impossible for lobha-hetu, dosa-hetu and moha-hetu not to develop and flourish.  No other dhamma except panna, which is amoha-hetu, can relinquish and eradicate akusala-hetu.  When one studies the dhamma and understand characteristics of realities that appear through the eyes, ears, nose, tongue, bodysense and mind, and becomes the person who develops sati-patthana, the kusala that is amoha or panna would slowly develop.  Once there is realization of the ariya-sacca-dhamma and one becomes the sotapanna-puggala, then akusala-dhamma would be eradicated type by type and level by level until one reaches the status of the arahanta.

 Those who attain the status of the ariya-puggala of the sotapanna, sakadagami and anagami levels are the sekkha-puggala, who must still further develop panna until there is eradication of both akusala-hetu and kusala-hetu because as long as there are kusala-hetu, there would still be paccaya for kusala- vipaka to arise endlessly.  The arahanta who has eradicated both akusala-hetu and kusala-hetu, whose citta, though arising with alobha, adosa, amoha, would be abyakata-hetu, and not hetu to cause vipaka to arise any further.  When will that day come?  That is possible one day if one perseveres to develop panna continually.  In the past there have been numerous persons who achieved those results, if it is something impossible to reach, there would not have been any.  But the result would not come as quickly as one hopes, they correspond with the hetu.  When panna has not arisen, or has not been developed, it cannot eradicate kilesa. Panna, in turn, must arise to be developed level by level respectively, to be able to fully realize the characteristics of realities until it is able to truly eradicate kilesa.

 Therefore, one should always remember that the study of citta, cetasika and rupa is toward the development of sati-patthana to know the characteristics of realities that are citta, cetasika and rupa that arise and appear at which instant in reality; not deviant in the slightest from what the Buddha was omniscient of and  manifested.  If one studied and understood one thing and practiced another, without directly knowing the characteristics of realities as they truly are exactly as one has studied, one could not eradicate kilesa.

 Akusala-hetu cannot be of any other jati.  No matter whether they are lobha-cetasika, dosa-cetasika or moha-cetasika that arise in an instant, they are of akusala-jati and paccaya for akusala-citta to arise at that instant as well as accumulate in continuation into the future.  But the three sobhana-hetu, namely 1) alobha-cetasika 2) adosa-cetasika 3) panna-cetasika can be of kusala-jati, vipaka-jati or kiriya-jati since alobha-cetasika, adosa-cetasika and panna-cetasika could arise with kusala-citta, kusala-vipaka or sobhana-kiriya-citta.  The term "sobhana" has a broader meaning than the word "kusala" because sobhana-dhamma are realities that are kusala, kusala-vipaka or sobhana-kiriya.  Therefore, since all dhamma are classified into 3 kinds: kusala-dhamma, akusala-dhamma and abyakata-dhamma, the 6 hetu-cetasika can be classified as 9 kinds of hetu:

 The 3 akusala-hetu,       namely 1) lobha-cetasika
                                                2) dosa-cetasika
                                                3) moha-cetasika
 The 3 kusala-hetu,         namely 1) alobha-cetasika
                                                2) adosa-cetasika
                                                3) panna-cetasika
 The 3 abyakata-hetu,     namely 1) alobha-cetasika
                                                2) adosa-cetasika
                                                3) panna-cetasika

1.  What paramattha-dhamma are hetu-paccaya?
2.  What is abyakata-hetu?  Which are they?
3.  What is abyakata-dhamma? Which are they?
4.  How are kusala-hetu and sobhana-hetu different?
5.  What are nahetu?  What are sahetuka?
6.  Which hetu-cetasika are ahetuka?  Which are sahetuka?
7.  Which akusala-citta is eka-hetuka?  Which are davi-hetuka?
8.  Can kusala-citta be eka-hetuka?
9.  Is phassa-cetasika hetu or nahetu?  Is it ahetuka or sahetuka?  Is it eka-hetuka, davi-hetuka or ti-hetuka?
10.  What are the 9 hetu?