असति प्रतिज्ञोपरोधो यौगपद्यमन्यथा ॥ २१ ॥
asati pratijñoparodho yaugapadyamanyathā || 21 ||
asati—If non-existence (of cause) be assumed; pratijña-uparodhaḥ—contradiction of the proposition; yaugapadyam—simultaneity; anyathā—otherwise.
21. If non-existence (of cause) be assumed, (the effects being produced in spite of it) (there will result) contradiction of their (Bauddhas’) proposition. Otherwise (there would result) simultaneity (of cause and effect).
If, to avoid the difficulty shown in the previous Sutra, the Bauddhas say that effects are produced without a cause, then they would contradict their own proposition that every effect has a cause. If on the other hand a cause be assumed, then we have to accept that the cause and effect exist simultaneously at the next moment, i.e. the cause lasts for more than one moment, as already shown in the last Sutra, which would falsify the doctrine of momentariness.