When we hear sound, sound must arise in order to appear.  Sound is a sankhara.  When we smell a smell, the smell must arise in order to appear.  Therefore smell is a sankhara.  (…)  All that arise are sankhara since they all are conditioned.  Whether or not we could see them, all realities that appear, whatever they are: anger, discontent or dissatisfaction.  They do exist, they arise though unseen, but whatever arises is a sankhara.

Therefore we must understand that sankhara is the reality that truly exists for which the Buddhist terminology uses the words 'dhamma' or 'dhatu'.  When we use the word 'dhatu' (element) everyone knows that it belongs to no one, and common to all.  For example lobha or attachment and clinging, when it arises, afterwards it falls away, there is no clinging that lasts forever.  Nor does dosa or discontentment stay for long, it arises and then ends. 

Things that arise from conditions and fall away thus belong to none whomever.  Whether it were seeing, just the seeing now (or wherever irrespective of brahma, heaven or hell planes), is something that exists, a reality that arises from conditions.  Seeing is a sankhara-dhamma.

One must then understand in the right order, beginning with the meaning of dhamma, and that all dhamma that arise are sankhara dhamma, whether nama dhamma or rupa dhamma.  This might be new vocabulary for beginners, but we should understand there are two different realities that truly exist, namely:

One kind of reality is unable to know or experience anything whatever, it includes hardness, sweetness, spiciness, sound or smell.  These realities do not feel, remember, they are neither happy nor unhappy.  They are dhamma of the rupa dhamma side.  Are they sankhara?  (…)  They are.

As for the nama dhamma, such as memory, love, hatred, and jealousy, these realities also exist. Are they sankhara?  They are.

We should then know from now on that to speak of the dhamma is to talk about realities, all that is appearing now arise because of conditions and are sankhara dhamma.

When we study the abhidhamma or the paramattha dhamma we would know that realities that truly exist consist of the citta paramattha, cetasika paramattha, rupa paramattha and nibbana paramattha.  No matter whether in the three Pitaka, in the world or the entire universe, there is nothing other than citta, cetasika and rupa that are conditioned realities.  When there are conditions, realities would arise either as nama dhamma or rupa dhamma.  Both rupa dhamma and nama dhamma that arise are sankhara dhamma of their respective kinds.  (…)

The term 'abhisankhara' means the reality that is predominant in conditioning composing or causing others to arise.  Therefore the predominant factor in causing us to be born distinctly is kamma, intending the cetana cetasika.  (…)  The sankhara in the paticasamuppada also refers to the cetana the abhisankhara, one of the 52 cetasika.