Ord. IV d. 11 q. 3 (whether the bread can be transubstantiated):
"To the first, I grant the first proposition, that of one being there is one act of being; but the second, that one act of being requires only one form, should be denied, by taking 'act of being (esse)' uniformly in the major and the minor. For just as being (ens) and one are divided into the simple and the composite, so also to be (esse) and to be one (or one 'to be': ita esse et unum esse) is distinguished into to be such and such; therefore to be (esse) per se one does not determine itself precisely simple (?? non determinat sibi esse simplex praecise), just as neither something divided determines for itself precisely the other of the dividing ones. In that way there is one act of being (esse) of the entire composite, and nevertheless it includes many partial acts of being, just as the total is one being (ens), and nevertheless has many partial entities. For I know not (nescio quid) that fiction, that esse is something supervening to a non-composed essence, if essence is composite.. In this way the esse of the entire composite includes the being (esse) of all the parts, and includes many partial esse's of many parts or forms, just as a total being (ens) from many forms includes thos partial actualities.
"If, nevertheless, there be made any force in speech, I grant that the formal esse of the total composite is principally through one form, and that form is that by which the total composite is this being, that however is the ultimate advening to all the preceding (forms); and in this way the total composite is divided into two essential parts, in its proper act, namely ultimate form, by which it is that which it is, and proper potency of that act, which includes prime matter with all the preceding forms. And in that manner I grant that that total being (esse) is completed by one form, which gives to the total that which it is. But from this it does not follow, that in that total is included precisely one form, or that in the total are included many forms, not just as specifically constituting that composite, but just as certain things included in the potentiality of that composite."
The wider context of this (if anyone is interested) is that of eucharistic conversion. Aquinas holds (and here Scotus agrees) that transubstantiation entails a conversion of the matter and the form of the bread into the matter and form of Christ. Scotus thinks Thomas's view is problematic because of the latters' thesis of the unicity of the substantial form. The identity of the terminus ad quem is supplied by the words of institution: the body of Christ. On Aquinas's view, the body of Christ is the term of the change and the soul is only present by natural concomitance, that is, what is present naturally in the body of Christ. But it isn't the term of the change. Aquinas tries to get around it with a clipped remark that since the intellective soul virtually contains all the lower functions, one of which is esse corporeum, this lower function can act in place of the soul. Scotus attacks this as insufficient due to the fact that the functions of the soul (on Aquinas's view) amount to only being distinct by reason and instead postulates that the terminus ad quem must instead be the forma corporeitatis of Christ.
One could ramble on all day about this stuff.