2. Analytical Introduction (5)

2.1.2. Logic as a speculative science

a) Preliminary notions

St Thomas distinguishes the speculative from the practical in this way:

As is said in The Soul: “Practical knowledge differs from speculative knowledge in its end.” For the end of speculative knowledge is simply truth, but the end of practical knowledge, as we read in the Metaphysics, is action.

Now, some knowledge is called practical because it is directed to a work. This happens in two ways. In the first way, it is directed in act—that is, when it is actually directed to a certain work, as the form is which an artist preconceives and intends to introduce into matter. This is called actual practical knowledge and is the form by which knowledge takes place. At other times, however, there is a type of knowledge that is capable of being ordered to an act, but this ordering is not actual. For example, an artist thinks out a form for his work, knows how it can be made, yet does not intend to make it. This is practical knowledge, not actual, but habitual or virtual.

At still other times, knowledge is utterly incapable of being ordered to execution. Such knowledge is purely speculative. This also happens in two ways. First, the knowledge is about those things whose natures are such that they cannot be produced by the knowledge of the knower, as is true for example, when we think about natural things. Second, it may happen that the thing known is something that is producible through knowledge but is not considered as producible; for a thing is given existence through a productive operation
QDV 3,3,c.

cf also SA 3,lect. 15, n. 820; SM 2,lect.2, nn. 290-291; I14,16,c; 79,11,c.

b) Thesis
1. statement: Logic, by reason of its principles, is instrumentally speculative, even though it implies a certain practical mode.

2. demonstration:
i) from the purpose of logic
m The scope of logic is to flee error, and therefore to know the truth fleeing error;
Mbut no science having truth for its scope is practical, but tends to knowledge through itself;
C Logic is therefore speculative
ad m Logic doesn't consider the products of reason ultimately as producible, but as ordered to knowledge; therefore it is instrumentally speculative (cf EBT 5,1,2m: "res autem de quibus est logica non quaeruntur ad cognoscendum propetr seipsas, sed ut adminiculum quoddam alias scientias".) and therefore possesses a practical mode: the proper goal of logic being knowing, one also tries to construct syllogisms, the scope of the science which produces these remains speculative.

ii) from the principles of logic
we may also anticipate the supreme principles of logic: "two things identical to a third are identical to one another"; "Everything said of a universal subject is said of all the particular subjects it comprises"; but these principles are purely speculative.