ing up against imported Greek philosophy. Ibn Sina’s fame-making project is
to amalgamate this alien heritage with the key dispute within Islamic rational
theology, the relation between God’s creative power and the fleeting substances
of the world. Ibn Sina’s cogito is a move to sharpen the sheer contingency of
created being, and thereby to produce a proof of God at hitherto unknown
levels of philosophical abstraction and reflexivity. Ibn Sina’s thought experi-
ment of a man flying in the dark, doubtful of everything about the bodily
world, is designed to show that being itself is always known, even if there is
doubt as to what kind of being it is. This sets the stage for Ibn Sina’s
distinctions among the sub-types of necessary, possible, and contingent being,
leading to a proof of God as being purely necessary in itself alone.
The case of Ibn Sina shows that the systematic use of doubt can be delib-
erately fostered in the clashes of intellectual life in order to uncover new levels
of abstraction. Until the revival of Aristotle in the mid-1200s, Augustine and
Ibn Sina (under the name Avicenna) were the two most influential imports in
medieval Christian philosophy. This is not surprising, given that they form the
two high points of the dominant Neoplatonic tradition, honed to epistemo-
logical acuteness by hostile confrontation with militant monotheism. Ibn Sina’s
use of doubt would be emulated even after the triumph of Christian Aris-
toteleanism; Duns Scotus drives beyond both Aquinas and Avicenna to yet
higher levels of metaphysical abstraction by pointing to univocal being, that
which we conceive of even if we are in doubt as to whether it is existence or
essence.
Generally speaking, the rationalistic lines of Islamic and Christian philoso-
phy have no use for omni-skepticism; Duns Scotus’s use of doubt is quite
limited and specific. A full-blown skepticism, together with the cogito, does
appear with the outburst of the nominalist movement in the 1300s. Here the
situation is more like the classic conditions for skepticism as a plague on all
houses, which typically arises when the attention space is crowded, and the
lines of rivalry have become set and show no sign of going away. Jean of
Mirecourt, in the height of the action at Paris in the 1340s, takes to an extreme
the nominalist tactic of undercutting Thomist and Scotist positions, and indeed
any rational propositions of theology. Mirecourt hits on the cogito, but as a
residual, the one item of knowledge that is secure because it passes the test of
resisting self-contradiction. Mirecourt was an offbeat character in medieval
Christian philosophy; his books were burned, and his doctrine was without
influence. Here the cogito acquires no fame because it has no system-generating
consequences. Mirecourt’s use is purely destructive.
In India, Shankara established a dominant reputation for the entire period
of post-Buddhist philosophy by a constructive use of the cogito. His is a
full-fledged use of omni-skepticism, to clear the decks of all worldly knowledge.
Sequence and Branch in the Social Production of Ideas^ •^815