The Magisterium teaches that there are three fonts or sources of morality, that is to say, three types of things that determine the morality of an act:
(2) moral object
If all three fonts are good, then the act is moral; it is not a sin; the act is at least morally licit (permissible). If any one or more fonts is bad, the act is immoral; it is a sin to commit such an act; the act is morally illicit.
FIRST FONT: The intended end (or purpose) for which the act is chosen.
SECOND FONT: The inherent ordering of the act itself toward its moral object. This ordering constitutes the moral species, i.e. the essential moral nature, of the chosen act.
THIRD FONT: The circumstances pertaining to the morality of the act, especially the reasonably anticipated good and bad consequences.
Catechism of the Catholic Church: “The morality of human acts depends on: — the object chosen; — the end in view or the intention; — the circumstances of the action. The object, the intention, and the circumstances make up the ‘sources,’ or constitutive elements, of the morality of human acts.”
Compendium of the Catechism: “The morality of human acts depends on three sources: the object chosen, either a true or apparent good; the intention of the subject who acts, that is, the purpose for which the subject performs the act; and the circumstances of the act, which include its consequences.”
USCCB Catechism: “Every moral act consists of three elements: the objective act (what we do), the subjective goal or intention (why we do the act), and the concrete situation or circumstances in which we perform the act…. All three aspects must be good — the objective act, the subjective intention, and the circumstances — in order to have a morally good act.”
All three fonts of morality must be good for an act to be moral.
Suppose that, in a particular hypothetical act, the intention is good, and the moral object is good. This act is done with only good intentions, and the act is not intrinsically evil. However, the act has bad consequences (harm) that can be reasonably anticipated at the time that the act is chosen. These bad consequences are not intended; they are unintended. Nevertheless, the act is chosen with the knowledge that these bad consequences, this harm, is likely to occur.
In this example, the first two fonts of morality are good. There is no bad intention of any kind. To intend a bad consequences as an end would be an immoral intention. But in this example, nothing bad or immoral is intended. There is no evil moral object. The chosen act is not that type of act called intrinsically evil, so there is nothing wrong with the moral species of the act.
Is all this sufficient to make the act moral? Certainly not.
The first two fonts are good, but we must still morally evaluate the third font: circumstances. This font takes into account “the totality of the foreseeable consequences of that act for all persons concerned” (Veritatis Splendor, n. 79.) If the reasonably anticipated (‘foreseeable’) bad consequences morally outweigh the reasonably anticipated good consequences, then the third font is bad and the act is immoral. It is always a sin to choose to act when you reasonably anticipate that your action will do more harm than good — even if that harm is unintended.
To be moral, all three fonts must be good. The fact that the bad consequences are unintended does not change the fact that the act is chosen in the knowledge that those bad consequences may occur. So if the person reasonably anticipates that those bad consequences outweigh any reasonably anticipated good consequences, the act is a sin. But if the person reasonably anticipates that those bad consequences are morally outweighed by the reasonably anticipated good consequences, then the third font is good.
Certainly, the moral weight of both the good and bad consequences is influenced by their degree of likelihood and their gravity. An unlikely consequence, good or bad, has less moral weight than a likely consequence. A grave bad consequence has more moral weight than a light good consequence. And if a bad consequence could not have been reasonably anticipated, then it does not enter into the moral evaluation of the third font at all.
But it is not true that reasonably anticipated bad consequences have no moral weight merely because they are unintended. The claim that unintended bad consequences cannot make an act immoral is contrary to the teachings of the Magisterium on ethics.