Objection 1. It would seem that precipitation is not a sin included in imprudence. Imprudence is opposed to the virtue of prudence; whereas precipitation is opposed to the gift of counsel, according to Gregory, who says (Moral. ii, 49) that the gift of "counsel is given as a remedy to precipitation." Therefore precipitation is not a sin contained under imprudence.
Objection 2. Further, precipitation seemingly pertains to rashness. Now rashness implies presumption, which pertains to pride. Therefore precipitation is not a vice contained under imprudence.
Objection 3. Further, precipitation seems to denote inordinate haste. Now sin happens in counselling not only through being over hasty but also through being over slow, so that the opportunity for action passes by, and through corruption of other circumstances, as stated in Ethic. vi, 9. Therefore there is no reason for reckoning precipitation as a sin contained under imprudence, rather than slowness, or something else of the kind pertaining to inordinate counsel.
On the contrary, It is written (Proverbs 4:19): "The way of the wicked is darksome, they know not where they fall." Now the darksome ways of ungodliness belong to imprudence. Therefore imprudence leads a man to fall or to be precipitate.
I answer that, Precipitation is ascribed metaphorically to acts of the soul, by way of similitude to bodily movement. Now a thing is said to be precipitated as regards bodily movement, when it is brought down from above by the impulse either of its own movement or of another's, and not in orderly fashion by degrees. Now the summit of the soul is the reason, and the base is reached in the action performed by the body; while the steps that intervene by which one ought to descend in orderly fashion are "memory" of the past, "intelligence" of the present, "shrewdness" in considering the future outcome, "reasoning" which compares one thing with another, "docility" in accepting the opinions of others. He that takes counsel descends by these steps in due order, whereas if a man is rushed into action by the impulse of his will or of a passion, without taking these steps, it will be a case of precipitation. Since then inordinate counsel pertains to imprudence, it is evident that the vice of precipitation is contained under imprudence.
Reply to Objection 1. Rectitude of counsel belongs to the gift of counsel and to the virtue of prudence; albeit in different ways, as stated above (Question 52, Article 2), and consequently precipitation is opposed to both.
Reply to Objection 2. Things are said to be done rashly when they are not directed by reason: and this may happen in two ways; first through the impulse of the will or of a passion, secondly through contempt of the directing rule; and this is what is meant by rashness properly speaking, wherefore it appears to proceed from that root of pride, which refuses to submit to another's ruling. But precipitation refers to both, so that rashness is contained under precipitation, although precipitation refers rather to the first.
Reply to Objection 3. Many things have to be considered in the research of reason; hence the Philosopher declares (Ethic. vi, 9) that "one should be slow in taking counsel." Hence precipitation is more directly opposed to rectitude of counsel than over slowness is, for the latter bears a certain likeness to right counsel.
Source: Summa Theologica (New Advent)