No, they cannot. The use of sexual devices (“sex toys” or “marital aids”), even in marriage, is gravely immoral. There are a number of reasons why this type of act is intrinsically evil and morally illicit.
First, this type of sexual act is non-unitive and non-procreative. And the Magisterium teaches that each and every sexual act in a marriage must be unitive and procreative. Thus, any sexual act which is inherently non-unitive or inherently non-procreative is intrinsically evil.
Second, a sexual act does not cease to be a sexual act, if climax is lacking. Such devices cannot be used as mere “stimulation” prior to the natural marital act. As explained in yesterday’s post (Q. 1), the normal performance of the marital sexual act itself does not justify “all the rest, in whatever way it is done”, not even acts done “in the preparation” (foreplay). And St. Alphonsus Liguori teaches that sodomy is still sodomy if climax is lacking (Moral Theology, On Matrimony, Book VI, Q. 916).
Third, the use of a sex toy is a type of masturbation, even when the person using the device is one’s spouse. And masturbation has been condemned by the ordinary and universal Magisterium as intrinsically evil and always gravely immoral.
Fourth, the use of sexual devices is specifically condemned by the Magisterium: Sacred Penitentiary, 3 June 1916, Denzinger 3638-40. The Sacred Penitentiary considers the situation in which a husband proposes to use a “artificial instrument” in a sexual act on his wife. The Sacred Penitentiary responds that this act is gravely immoral, and that the wife may not consent, nor even offer only passive resistance.
“Questions: 1. Is a wife, when her husband wishes to practice onanism by means of an (artificial) instrument, required to exercise positive resistance?”
The term “onanism” is used here to refer to masturbation. Sometimes onanism refers to contraception. Other times it refers to masturbation, even by a female. Both contraception and masturbation are similar to the sin of Onan in the Bible. In some cases, the onanism can refer, more broadly, to a range of unnatural sexual acts between a man and a woman. In his article The Sin of Onan Revisited, Fr. Brian W. Harrison explains:
” ‘Onanism’, the term derived from Genesis 38:9-10 which in traditional Christian usage has designated both masturbation and unnatural intercourse between a man and woman, is not exactly a pleasant theme to write about.”
“The classical Jewish commentators — who can scarcely be accused of ignorance regarding Hebrew language, customs, law, and biblical literary genres — certainly saw in this passage of Scripture a condemnation of both unnatural intercourse and masturbation as such.”
Onan’s sin is sometimes used to refer to contraception, or to unnatural sexual acts between man and woman, or to masturbation, since all these acts are “intrinsically sterile forms of genital activity” (as Fr. Harrison notes in his article). If you look up “Onanism” in Denzinger’s index, it says “See Contraception; Masturbation”.
So the term “onanism”, in the Denzinger quote above, refers to an unnatural sexual act committed on a wife, by her husband, by means of an instrument (i.e. a sex toy, such as a vibrator or phallic device). This can be considered a type of masturbation, specifically, but in any case it is an unnatural sexual act — an intrinsically non-procreative form of sexual activity.
The answer given by the Sacred Penitentiary, across three questions on this subject, is that the act is gravely immoral, and the wife must offer active resistance, not merely passive resistance. The answer to the third question reveals that this act is morally equivalent to an aggressor who is attempting to rape a virgin.
However the question itself does not concern rape, but whether the wife may consent to this act. She cannot morally consent. The act is so gravely immoral that she must offer active resistance. And this implies that a wife cannot use such an instrument on herself, nor on her husband. All such sexual acts are gravely immoral. They are unnatural sexual acts, because they are non-procreative and non-unitive.
Notice that this act is so gravely immoral that it is compared to the rape of a virgin. Certainly, then, the act does not become moral by being done in the context of the natural marital act (just as yesterday’s post proves). And it does not become moral if climax is lacking, just as rape does not become moral if climax is lacking.
What kind of person writes a book encouraging Catholic spouses to use such shameful devices, within the Sacrament of holy Matrimony, while calling these acts “holy sex”? And how badly would someone else have to misunderstand the ethical teachings of the Church, to write words of praise promoting such a book? But I suspect a few promoters of this behavior know that these acts are unnatural and contrary to the traditional moral teachings of the Church, but they publicly approve the behavior anyway, in order to please their readers.
More on marital chastity in my book: The Catholic Marriage Bed
Please take a look at this list of my books and booklets, and see if any topic interests you.