“Omnipotence is the ground for acting on anything and for producing whatever is possible, even if per impossible God were not everywhere…God’s omnipotence does not necessarily entail that he is everywhere according to his essence”
So said Duns Scotus in Ord., I.d. 37.q. un., n. 7 in Opera Omnia (I am working very much on Richard Cross’s chapter in Angels in Medieval Philosophical Inquiry here and have copied his citation).
This no doubt sounds strange at first, but one must understand that Scotus speaks here of omnipresence in a very particular sense and according to a specific concept. As is made clear at the end, he is speaking of omnipresence specifically according to essence.
To quote Cross at length here:
Scotus of God’s presence ‘according to essence’, and this is a reference to a well-known distinction, found in Peter Lombard and with earlier antecedents, between God’s being somewhere ‘by power, presence and essence’. Aquinas–to take an obvious example explicitly criticized in this context by Scotus–tends to see all of these kinds of presence in causal terms. Existing somewhere by power is straightforwardly causal. Aquinas reasons that a king–perhaps an absolute monarch–can be causally present throughout his kingdom without being present throughout it in any stronger sense: he is causally present by causing effects irrespective of his spatial relation to the effects. (A king can do things by means of his ministers, for example.) For something to exist somewhere by presence is for the place occupied to be subject to inspection by the thing so located. And an object is said to be present by essence wherever its substance is. In this case of God, this last sort of presence is reducible to a causal sort of presence: ‘God is in all things through his essence in so far as he is present to all as the cause of being’. God’s substantial presence–his presence ‘according to essence’–is here distinguished from his presence ‘by power’ merely in terms of its generality. There is no sense in Aquinas that it is a fundamentally different kind of presence, and it is for this reason that omnipotence immediately entails immensity.
Thomas says in his Summa:
And in the SCG:
For, the mover and the thing moved must be simultaneous, as the Philosopher proves. But God moves all things to their operations, as we have shown. Therefore, He is in all things.
Scotus’s charge is going to be that Thomas is ambiguous here and does not seem to sufficiently distinguish omnipresence by essence from omnipresence by power since both are essentially causal.
Scotus takes this question up in his discussion on the mode of angelic presence. Whereas Thomas argues that angels are said to be in a place solely by means of operation, Scotus holds that they are in a place also (and primarily) by essence. In order to argue against this conclusion, Scotus begins with what Thomas himself says about God’s presence (the thought being that this is relevant to the question because “it seems less true of God that he must by his essence be present in the place where he operates than of an angel”). Scotus offers two possible readings of Thomas here. On the first reading, Thomas essentially reduces God’s presence to His causal activity and so proves nothing with the above quotations. On the second reading, a distinction is made between God’s presence by essence and His operations and so, Scotus argues, Thomas is inconsistent in not applying this also to the mode of angelic presence:
He who posits this conclusion contradicts himself, because in the question 'whether God is everywhere' [Aquinas SG 3.68] he proves that God is everywhere through the fact that, according to the Philosopher Physics 7.2.243a3-4, 'the mover is together with the moved', and God is the first efficient cause and therefore able to move every movable; and from this he concludes that God is in everything and present to everything. I ask what he means hereby to conclude. Either that God is present, that is, is 'mover', and then there is a begging of the question because the premises and the conclusion are the same [sc. 'because God moves everything, therefore he is present by motion to everything']; and is nothing to the purpose, because he intends there to infer the immensity of God from the presence of God to everything. Or he means to infer the presence that belongs to God insofar as he is immense, and in that case from God's presence anywhere is inferred - according to him - the presence that pertains to the divine immensity (which belongs to God insofar as he is God), such that God will as he is immense naturally be present before he is as operating present; and this is inferred from the fact that he is present by operation, the way the prior is inferred from the posterior [sc. as cause is inferred from effect, or 'God is somewhere by operation, therefore he is first there by essence']. Therefore by likeness as to the issue at hand, an angel will naturally be present in some place by essence before he is present there by his operation [sc. contrary to the opinion in question here, which says an angel is only present in place by operation and not first by essence]. (http://www.logicmuseum.com/wiki/Authors/Duns_Scotus/Ordinatio/Ordinatio_II/D2/P2Q2)
Thus, for Scotus there is a clear difference between God’s presence by way of power and effect and his presence by way of essence. Francis Turretin in his section on the omnipresence of God makes this same distinction rather clearly:
God may be said to be present with all things in three modes: (1) by power and operation; (2) by knowledge; (3) by essence. This is usually expressed by the Scholastics in the line: Inter, praesenter Deus est, et ubique patenter ("Meanwhile, God is present, and everywhere powerfully"). He is said to be everywhere by his power because he produces and governs all things and works all things in all (in which sense Paul says, "In him we live and move and have our being," Acts 17:28). He is present with all by his knowledge because he sees and beholds all things which are and become in every place as intimately present to and placed before him. Hence "all things” are said "to be naked and open unto the eyes of him" and "there is no creature that is not manifest in his sight" (Heb. 4:13 ). Finally, he is everywhere by his essence because his essence penetrates all things and is wholly by itself intimately present with each and everything. Now it is of this last presence we properly treat here, for our adversaries themselves do not deny that God is everywhere present by his power and knowledge (as has been said already).
And
But the orthodox believe and confess the immensity and omnipresence of God, not only as to virtue and operation, but principally as to essence.
With this, Scotus’s affirmation at the start of this post becomes clear: there is nothing about the ubiquity of God that necessarily entails His omnipotence, His ability to produce whatever is possible. The two concepts do not formally entail one another. One can only reason from omnipresence to omnipotence if one has in mind God’s omnipresence according to power.
From what I can tell, the Reformed followed through on this clear Scotist distinction between essence and operation when it came to angelic presence as well. Thus Turretin speaks of the presence of angels, saying:
Whatever is finite, for that very reason, ought to be bounded by its own certain "where," i.e., may be so here as not to be there. Nor can virtual presence be separated here from substantial, since the former necessarily supposes the latter as its principle. For as to operate supposes existence, so every cause ought to be where it operates. However, although the presence of angels may be known a posteriori from their operation, it does not follow that the whole relation of presence consists in operation alone, since it is not always necessary for it to operate at least outwardly. Nor is it more absurd for an angel to be somewhere by essence than by operation, since both are spiritual.
And Petrus Van Mastricht says likewise:
Third, the place of their existing, which they occupy not only by reason of their operating, but by coexistence; nor by circumscription, as if they were bounded extrinsically, like bodies; nor by repletion, or infinite coexistence; but by delimitation, whereby on account of the finitude of their essence, they are so restricted to this place that they may not be in a different one. Thus it is said that in one man there was a legion (Luke 8:30).
Voetius follows the same opinion in his Syllabus of Theological Questions but I am too lazy to find the exact place, so just trust me bro.