Objection 1. It would seem that it is lawful to grant spiritual things in return for an equivalent of service, or an oral remuneration. Gregory says (Regist. iii, ep. 18): "It is right that those who serve the interests of the Church should be rewarded." Now an equivalent of service denotes serving the interests of the Church. Therefore it seems lawful to confer ecclesiastical benefices for services received.
Objection 2. Further, to confer an ecclesiastical benefice for service received seems to indicate a carnal intention, no less than to do so on account of kinship. Yet the latter seemingly is not simoniacal since it implies no buying or selling. Therefore neither is the former simoniacal.
Objection 3. Further, that which is done only at another's request would seem to be done gratis: so that apparently it does not involve simony, which consists in buying or selling. Now oral remuneration denotes the conferring of an ecclesiastical benefice at some person's request. Therefore this is not simoniacal.
Objection 4. Further, hypocrites perform spiritual deeds in order that they may receive human praise, which seems to imply oral remuneration: and yet hypocrites are not said to be guilty of simony. Therefore oral remuneration does not entail simony.
On the contrary, Pope Urban [Urban II, Ep. xvii ad Lucium] says: "Whoever grants or acquires ecclesiastical things, not for the purpose for which they were instituted but for his own profit, in consideration of an oral remuneration or of an equivalent in service rendered or money received, is guilty of simony."
I answer that, As stated above (Article 2), the term "money" denotes "anything that can have a pecuniary value." Now it is evident that a man's service is directed to some kind of usefulness, which has a pecuniary value, wherefore servants are hired for a money wage. Therefore to grant a spiritual thing for a service rendered or to be rendered is the same as to grant it for the money, received or promised, at which that service could be valued. If likewise, to grant a person's request for the bestowal of a temporary favor is directed to some kind of usefulness which has a pecuniary value. Wherefore just as a man contracts the guilt of simony by accepting money or any eternal thing which comes under the head of "real remuneration," so too does he contract it, by receiving "oral remuneration" or an "equivalent in service rendered."
Reply to Objection 1. If a cleric renders a prelate a lawful service, directed to spiritual things (e.g. to the good of the Church, or benefit of her ministers), he becomes worthy of an ecclesiastical benefice by reason of the devotion that led him to render the service, as he would by reason of any other good deed. Hence this is not a case of remuneration for service rendered, such as Gregory has in mind. But if the service be unlawful, or directed to carnal things (e.g. a service rendered to the prelate for the profit of his kindred, or the increase of his patrimony, or the like), it will be a case of remuneration for service rendered, and this will be simony.
Reply to Objection 2. The bestowal of a spiritual thing gratis on a person by reason of kinship or of any carnal affection is unlawful and carnal, but not simoniacal: since nothing is received in return, wherefore it does not imply a contract of buying and selling, on which simony is based. But to present a person to an ecclesiastical benefice with the understanding or intention that he provide for one's kindred from the revenue is manifest simony.
Reply to Objection 3. Oral remuneration denotes either praise that pertains to human favor, which has its price, or a request whereby man's favor is obtained or the contrary avoided. Hence if one intend this chiefly one commits simony. Now to grant a request made for an unworthy person implies, seemingly, that this is one's chief intention wherefore the deed itself is simoniacal. But if the request be made for a worthy person, the deed itself is not simoniacal, because it is based on a worthy cause, on account of which a spiritual thing is granted to the person for whom the request is made. Nevertheless there may be simony in the intention, if one look, not to the worthiness of the person, but to human favor. If, however, a person asks for himself, that he may obtain the cure of souls, his very presumption renders him unworthy, and so his request is made for an unworthy person. But, if one be in need, one may lawfully seek for oneself an ecclesiastical benefice without the cure of souls.
Reply to Objection 4. A hypocrite does not give a spiritual thing for the sake of praise, he only makes a show of it, and under false pretenses stealthily purloins rather than buys human praise: so that seemingly the hypocrite is not guilty of simony.
Source: Summa Theologica (New Advent)