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.” (CCC, n. 1750.)
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.” (Compendium, n. 367.)
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.” (United States Catholic Catechism for Adults, p. 311-312.)
Pope John Paul II: “The doctrine of the object as a source of morality represents an authentic explicitation of the Biblical morality of the Covenant and of the commandments, of charity and of the virtues. The moral quality of human acting is dependent on this fidelity to the commandments, as an expression of obedience and of love. For this reason – we repeat – the opinion must be rejected as erroneous which maintains that it is impossible to qualify as morally evil according to its species the deliberate choice of certain kinds of behaviour or specific acts, without taking into account the intention for which the choice was made or the totality of the foreseeable consequences of that act for all persons concerned.” (Veritatis Splendor, n. 82.)