The
conditions that arise from the mind, such as thought-formations, appear
and vanish, again and again. Here I’m referring to the rippling of the
mind. When the mind ripples, that’s the formation of a thought. Labels,
which deal with conjecturing, memorizing, and recognizing, are termed
sañnā. ‘Long’ thoughts are sañnā; short thoughts are saṅkhāra. In other
words, when a thought forms—‘blip’—that’s a saṅkhāra. Sañnā refers to
labeling and recognizing. Viññāṇa refers to the act of
taking note when anything external comes and makes contact with the
senses, as when visible forms make contact with the eye and cognition
results. All of these things are constantly arising and vanishing of
their own accord, and so the Buddha called them khandhas. Each ‘heap’ or
‘group’ is called a khandha. These five heaps of khandhas are
constantly arising and vanishing all the time.

“Monks,
before my self-awakening, when I was still just an unawakened
bodhisatta, the realization came to me: ‘How this world has fallen on
difficulty! It is born, it ages, it dies, it falls away & rearises,
but it doesn’t discern the escape from this stress, from this aging
& death. O when will it discern the escape from this stress, from
this aging & death?’