Objection 1. It would seem that foresight should not be accounted a part of prudence. For nothing is part of itself. Now foresight seems to be the same as prudence, because according to Isidore (Etym. x), "a prudent man is one who sees from afar [porro videns]": and this is also the derivation of "providentia [foresight]," according to Boethius (De Consol. v). Therefore foresight is not a part of prudence.
Objection 2. Further, prudence is only practical, whereas foresight may be also speculative, because "seeing," whence we have the word "to foresee," has more to do with speculation than operation. Therefore foresight is not a part of prudence.
Objection 3. Further, the chief act of prudence is to command, while its secondary act is to judge and to take counsel. But none of these seems to be properly implied by foresight. Therefore foresight is not part of prudence.
On the contrary stands the authority of Tully and Macrobius, who number foresight among the parts of prudence, as stated above (Article 48).
I answer that, As stated above (47, 1, ad 2, 6,13), prudence is properly about the means to an end, and its proper work is to set them in due order to the end. And although certain things are necessary for an end, which are subject to divine providence, yet nothing is subject to human providence except the contingent matters of actions which can be done by man for an end. Now the past has become a kind of necessity, since what has been done cannot be undone. On like manner, the present as such, has a kind of necessity, since it is necessary that Socrates sit, so long as he sits.
Consequently, future contingents, in so far as they can be directed by man to the end of human life, are the matter of prudence: and each of these things is implied in the word foresight, for it implies the notion of something distant, to which that which occurs in the present has to be directed. Therefore foresight is part of prudence.
Reply to Objection 1. Whenever many things are requisite for a unity, one of them must needs be the principal to which all the others are subordinate. Hence in every whole one part must be formal and predominant, whence the whole has unity. Accordingly foresight is the principal of all the parts of prudence, since whatever else is required for prudence, is necessary precisely that some particular thing may be rightly directed to its end. Hence it is that the very name of prudence is taken from foresight [providentia] as from its principal part.
Reply to Objection 2. Speculation is about universal and necessary things, which, in themselves, are not distant, since they are everywhere and always, though they are distant from us, in so far as we fail to know them. Hence foresight does not apply properly to speculative, but only to practical matters.
Reply to Objection 3. Right order to an end which is included in the notion of foresight, contains rectitude of counsel, judgment and command, without which no right order to the end is possible.
Source: Summa Theologica (New Advent)