into existence twice, and this is the view of Buddhaghosa who says
that the first two links (ignorance and the sankharas) belong to past
time and explain the present existence: the next eight (consciousness to
existence) analyse the present existence: and the last two (birth and
old age) belong to future time, representing the results in another
existence of desire felt in this existence. And that is perhaps what the
constructor of the formula meant. It is clearest if taken backwards.
Suppose, the Buddha once said to Ananda[446], there were no birth, would
there then be any old age or death? Clearly not. That is the meaning of
saying that old age and death depend on birth: if birth were
annihilated, they too would be annihilated. Similarly birth depends on
Bhava which means becoming and does not imply anything self-existent and
stationary: all the world is a continual process of coming into
existence and passing away. It is on the universality of this process
that birth (jati) depends. But on what does the endless becoming itself
depend? We seem here on the threshold of the deepest problems but the
answer, though of wide consequences, brings us back to the strictly
human and didactic sphere. Existence depends on Upadana. This word means
literally grasping or clinging to and should be so translated here but
it also means fuel and its use is coloured by this meaning, since
Buddhist metaphor is fond of describing life as a flame. Existence
cannot continue without the clinging to life, just as fire cannot
continue without fuel[447].

The clinging in its turn depends on Tanha, the thirst or craving for
existence. The distinction between tanha and upadana is not always
observed, and it is often said tanha is the cause of karma or of sorrow.
But, strictly speaking, upadana is the grasping at life or pleasure:
tanha is the incessant, unsatisfied craving which causes it. It is
compared to the birana, a weed which infests rice fields and sends its
roots deep into the ground. So long as the smallest piece of root is
left the weed springs up again and propagates itself with surprising
rapidity, though the cultivator thought he had exterminated it. This
metaphor is also used to illustrate how tanha leads to a new birth.
Death is like cutting down the plant: the root remains and sends up
another growth.

We now seem to have reached an ultimate principle and basis, namely, the
craving for life which transcends the limits of one exist