2. Marriage and the end of ‘begetting and bringing up children’

According to traditional natural law accounts, marriage is the ‘society of a man and a woman, entered upon to produce and bring up offspring’ (Achenwall Reference Achenwall1763/Reference Achenwall and Kleingeld2020: bk. II, §44).Footnote ⁵ It is a central tenet of Kant’s account of marriage that he rejects this view. While Kant agrees with other natural law authors in holding that marriage can only take place between ‘two persons of different sexes’, procreation does not form part of his definition of marriage (RL §24, 6: 277.24–6, quoted below). Rather, Kant argues that spouses, from the standpoint of right, do not have to pursue the ‘end of begetting and bringing up children’: ‘it is not requisite for human beings who marry to make this their end in order for their union to be compatible with rights’ (6: 277.26–30; Kant’s emphasis).

Kant rejects the traditional link between marriage and procreation because it runs counter to the lifelong duration of marriage: if it were required for spouses to pursue the end of begetting and bringing up children, Kant argues, ‘marriage would be dissolved when procreation ceases’ (6: 277.31–2). Such a view is found, for instance, in Locke’s account of marriage. According to Locke, natural law permits the dissolution of marriage once no more children are produced and all existing children have been brought up to maturity (Locke Reference Locke1996: Second Treatise, §81).Footnote ⁶ Similarly, for Christian Wolff, marriage may be dissolved if the spouses are unable to produce offspring and if no children have yet been conceived (Wolff Reference Wolff1754: §871).

For Kant, in contrast, marriage necessarily has to be lifelong. He accordingly defines marriage as ‘the union of two persons of different sexes for lifelong possession of each other’s sexual attributes’ (RL §24, 6: 277.24–6; my emphasis). The lifelong duration is one of the properties of marriage that make it the (only) sexual union ‘in accordance with law’ (6: 277.24). That marriage alone is a sexual union that conforms to law means that agents ‘must necessarily marry’ if they want to have sex with each other (6: 278.1–3). Kant’s justification for the necessity of marriage is that only marriage can avert the danger of sexual objectification, that is, only in marriage can agents have sex without becoming mere objects of each other’s sexual desire (RL §25, 6: 278.15–17).Footnote ⁷ The reason is that marriage involves the reciprocal possession of each other’s person:

The reciprocal possession means that the relationship is exclusive. The right to a person akin to a right to a thing involves the possession of the other person ‘as a thing’ (RL §22, 6: 276.19–20). Thus, just as a right to a thing is ‘a right to the private use’ of it (RL §11, 6: 260.33–261.1), so a right to a person akin to a right to a thing means that one may ‘use’ the other person exclusively.

Only in an exclusive relationship can the danger of sexual objectification be averted, according to Kant. And in order for the spouses not to become mere objects of each other’s sexual desire, the relationship must be exclusive also over time, that is, it must be lifelong. Otherwise, the partners could arbitrarily exchange each other for somebody else, which would make them mere objects of their sexual desire, just as in non-marital intercourse. As Kant states in the Metaphysics of Morals Vigilantius:

Thus, for Kant, for sex to be in conformity with the right of humanity, it must take place within a lifelong, exclusive (i.e. monogamous) legal relationship. If a relationship fulfils these conditions, it is a sexual union ‘in accordance with law’ (RL §24, 6: 277.24). Insofar as the requirement to pursue the end of begetting and bringing up offspring would mean that a relationship would lose its legal validity if this end can no longer be attained, that requirement would indeed run counter to the lifelong duration of marriage, which is essential to its function of averting sexual objectification. In this way, Kant also argues in the Metaphysics of Morals Vigilantius:

Apart from the argument from the necessary lifelong duration of marriage, there is, in addition, a more general reason why, for Kant, marriage right cannot require the pursuit of the end of procreation. This reason is that Kantian right regulates external actions only and abstracts from inner, subjective conditions such as the agent’s subjective ends: ‘The concept of right … has to do … only with the external and indeed practical relation of one person to another’, and ‘no account at all is taken of the matter of choice, that is, of the end each has in mind’ (RL §B, 6: 230.7–10, .16–17). Thus Kant argues that marriage has to be a ‘[n]atural sexual union’, that is, a relationship in which ‘procreation of a being of the same kind is possible’ (RL §24, 6: 277.14–15). But whether the partners want to have children or not is not a question of right, nor is the fact whether the partners are indeed able to have children or not. Marriage as a legal, and hence merely external, relationship between two persons is indifferent in this regard. Hence, from the standpoint of right, married people can have sex without pursuing, or being able to pursue, the end of procreation.

In this regard, Kant decisively deviates from what we find in traditional natural law accounts of marriage. Thus, according to Pufendorf, any use of one’s sexual organs that deviates from the natural purpose of procreation ‘is repugnant to natural law’ (Pufendorf Reference Pufendorf1673/Reference Pufendorf and Tully1991: bk. II, ch. 2, §2). Similarly, for Wolff, ‘any sexual intercourse desired solely for the sake of lust … is impermissible’ (Wolff Reference Wolff1736: §23; cf. also Reference Wolff1754: §854). And according to Achenwall, ‘all use of the genitals for the sake of mere pleasure … goes against the natural divine law’ (Achenwall Reference Achenwall1763/Reference Achenwall and Kleingeld2020: bk. II, §44). Kantian right, in contrast, permits sexual intercourse without the aim or without even the chance of procreation.Footnote ⁹

3. The casuistical question regarding non-procreative sex

As noted above, Kant in the Doctrine of Right holds that sexual intercourse in marriage is permissible even when procreation is not possible. In the Doctrine of Virtue, Kant returns to this issue, but from an ethical perspective.

The premise of §7 of the Doctrine of Virtue is that the natural end of sexual inclination (‘sexual love’ [Liebe zum Geschlecht]) is the preservation of the species (6: 424.12–14). The overarching question of TL §7 is whether this fact implies any moral requirements with respect to sexual actions, and if so, what these requirements are:

In the main text of TL §7, Kant argues that masturbation is ‘a violation of duty to oneself’ because ‘by it the human being surrenders his personality (throwing it away), since he uses himself merely as a means to satisfy an animal impulse’ (6: 425.21–6). As Kant argues, insofar as masturbation is a use of one’s sexual capacity that deviates from the natural end of the preservation of the species, it serves merely to generate animal pleasure; and insofar as the agent subjects the humanity in his own person to his animal desire, masturbation implies treating oneself merely as a means. In Kant’s eyes, it amounts to ‘defiling oneself by lust’, as the title of TL §7 has it.Footnote ¹⁰

As with the majority of duties discussed in the Doctrine of Virtue, a section entitled ‘Casuistical Questions’ follows the main text of TL §7.Footnote ¹¹ As Kant says in the Doctrine of Method, casuistical questions serve an important function in moral education as they allow pupils to test their understanding of what duty demands; they thus facilitate the cultivation of moral reasoning (6: 483.32–484.4). Given this, two points should be noted.

First, as Rudolf Schuessler has shown, casuistical questions should not be confused with casuistry. Kant poses casuistical questions with respect to perfect as well as imperfect duties, but he is clear in that casuistry relates to imperfect duties only (TL, Introduction XVII, 6: 411.10–17). Imperfect duties admit of latitude and thus require casuistry. As Schuessler puts it, for Kant, casuistry is ‘an art of finding submaxims for the exercise of imperfect duties’ (Schuessler Reference Schuessler2021: 1003). Casuistical questions, in contrast, are ‘mainly classroom exercises to test whether pupils have acquired sufficient knowledge of ethics’ (Schuessler Reference Schuessler2021: 1003). Thus, the fact that Kant poses casuistical questions does not itself imply that he assumes any leeway in the exercise of the duty in question.

Secondly, the fact that Kant poses casuistical questions without answering them directly does not imply that he does not have a ready answer. As Kant says in the Doctrine of Method, casuistical questions serve to test the pupils’ moral understanding with ‘tricky’ (verfängliche) problems (6: 483.36). Kant regards this as a good way of teaching morals insofar as ‘questions about what one’s duty is can be decided far more easily than speculative questions’ (6: 484.1–2). Kant thus assumes that there are correct solutions to these problems. In the case of perfect duties, the casuistical questions, Schuessler argues, ‘are meant to elicit the response that such duties do not allow for exceptions even in apparently hard cases’ (Schuessler Reference Schuessler2021: 1003). Our further discussion will confirm this result.Footnote ¹²

In the section ‘Casuistical Questions’ which is appended to TL §7, Kant turns to the ‘natural’ use of one’s sexual capacities, namely, heterosexual intercourse. At the beginning, Kant recapitulates the main point of the main part of TL §7, according to which deviating from the natural end of procreation runs counter to duty. He then poses the question whether the natural end of procreation gives rise to further limitations with respect to ‘natural’ intercourse within marriage:

Note that Kant does not ask whether married couples should actively pursue the begetting of children. Indeed, Kant rejects such a requirement. Agents do not act contrary to duty, they do not violate their humanity if they do not promote the natural end of procreation:Footnote ¹³

Thus, the question that Kant poses in TL §7 is only whether married couples should refrain from having sex if procreation is not possible. As Kant goes on:

Kant’s question is thus whether marital intercourse that cannot serve the natural end of procreation would amount to the violation of a duty to oneself just as masturbation does.

The cases of pregnancy (which is the case that Plessing mentions in his letter: 10: 376.2) and of the wife’s sterility are clear enough. But what does Kant mean by the case that the wife ‘feels no desire for this’ (keinen Anreiz dazu bei sich findet)? At first glance, the case seems ‘strikingly different from the case of sex during non-fertile periods’ (Timmons Reference Timmons, Trampota, Sensen and Timmermann2013: 240 n. 27), and many commentators pass over this case when discussing the passage (e.g. Byrd Reference Byrd, Denis and Sensen2015: 169 n. 25; Mellin only quotes the first cases and substitutes an ‘etc.’ for the case at hand: Mellin Reference Mellin1799: 196). However, it becomes clear why Kant includes this case when one takes into account the medical knowledge of the time. Until the end of the eighteenth century, even among medical professionals, it was widely held that female orgasm was a prerequisite for conception.Footnote ¹⁴ Kant shares this view, as can be seen in the Religion, where he articulates the thesis that ‘natural generation cannot take place without sensual pleasure on both sides’ (6: 80.16–17).Footnote ¹⁵

Against this backdrop, the case of a lack of desire on the woman’s part could mean that she has no desire for intercourse on that specific occasion,Footnote ¹⁶ which is how the passage is commonly read (see e.g. Soble Reference Soble2003: 68; Mertens Reference Mertens2014: 338–9).Footnote ¹⁷ The case would thus be that the female partner lacks sufficient sexual desire on that occasion for conception to occur. However, in analogy to the case of sterility, Kant may also have thought of the case where the woman generally lacks a desire for sexual activity. This is how Tieftrunk, in his contemporary commentary on the Doctrine of Virtue, understands the passage. He paraphrases the case at hand such that the wife is ‘devoid of feeling’ (gefühllos) (Tieftrunk Reference Tieftrunk1798: 255), and he also speaks of ‘insensitivity’ (Unempfindlichkeit) (Tieftrunk Reference Tieftrunk1798: 257).Footnote ¹⁸ However one reads the – without doubt problematic – passage, Kant is clearly concerned with cases in which procreation is not possible.Footnote ¹⁹

After having raised the question whether marital intercourse that cannot lead to procreation is against duty, Kant points out that there could be a permissive law that would allow such intercourse:

Regarding the ‘still greater violation’ Kant may have thought of adultery, which according to the Collins lecture notes is ‘of all betrayals and breaches of faith … the greatest, since there is no promise more important than this’ (27: 390.28–30).Footnote ²⁰ Or Kant may have thought of masturbation, the topic of the main part of TL §7 and which according to him is ‘a defiling (not merely a debasing) of the humanity in [one’s] own person’ (6: 424.28–9).Footnote ²¹

While the first (partFootnote ²² of the) question, quoted further above, suggests a restrictive answer (it seems as if unpurposive sex runs counter to duty), the second suggests a permissive answer. Kant does not provide an explicit answer to the question, and the way he presents the question seems to leave open what he thinks about it. It could be that he thinks that sex in the cases mentioned is against duty. But it could likewise be that he thinks that there is a permissive law, as most interpreters think. Finally, it could be that he leaves the question altogether unanswered, as some commentators believe (see the references in the introduction).

Both the restrictive and the permissive alternatives that Kant articulates reflect common views of the time.Footnote ²³ As regards the first, we have already seen that prominent natural law authors hold that sex even within marriage is permissible only for the sake of procreation (see section 2). Similarly, Christian August Crusius, whose ethics Kant also engages with, argues in his Anweisung vernünftig zu leben that sex ‘without the lawful purpose of producing children … is contrary to divine intentions and therefore sinful and vain’ (Crusius Reference Crusius1744: §570). According to the restrictive view, non-procreative sex within marriage is just as wrong as ‘unnatural’ sex.

The argument that Kant presents for the purported existence of a permissive law reflects an argument that can be traced back to Paul’s first letter to the CorinthiansFootnote ²⁴ and was a common trope in the discussion of marriage in the eighteenth century (see Zedler 1732–Reference Zedler1750: s.v. ‘Ehestand’, vol. 8, col. 365–6).

Although Paul suggests that it is fundamentally best to live a celibate life, he argues that, given our nature, it is better for many people to marry and to also have regular intercourse with their spouse, for otherwise, there is a constant danger of falling into fornication:

While the celibate life is clearly best, Paul argues that it is allowed to marry and to regularly have sex in order to prevent burning with lust and becoming a victim of Satan. Note that Paul explicitly formulates this as a concession: the celibate life is what is, as such, religiously, hence ethically, demanded, but one may choose to marry if one cannot overcome one’s sexual desire.

Reference to Paul’s argument was widespread in the eighteenth century, for example to enable people who were obviously incapable of procreation to enter into marriage (for instance, for soldiers who were wounded in combat in a way that precluded them from producing offspring; see Buchholz Reference Buchholz1988: 420–21), and it was also common to refer to Paul when arguing that the, or at least one, end of marriage is the satisfaction of sexual desire in order to prevent fornication (see e.g. Hommel Reference Hommel1764: 38–9 and Reference Hommel1773: 38, 56–7; cf. also Hupel Reference Hupel1771: 20, 52).

Kant’s formulation of the second (part of the) question seems to suggest that he adopted the Pauline argument. As I shall go on to argue, however, it becomes clear on closer inspection that Kant does not adopt this line of argument himself but merely refers to it. Kant, as the following analysis shows, in fact takes a restrictive stance.

4. The ethical status of ‘unpurposive’ intercourse

A first piece of evidence that speaks against the view that Kant, in the Doctrine of Virtue, would adopt a permissive stance on non-procreative sex can be found in the main part of TL §7: the ‘rational proof’ that Kant presents to show that ‘unnatural’ sex is a violation of duty is not in fact limited to this, but is rather meant to also hold for the ‘even merely unpurposive[] use of one’s sexual attribute’ (6: 425.20–21; my emphasis).Footnote ²⁵ This means that not only in the case of sex that is ‘unnatural’ or ‘contrapurposive[]’ (6: 425.20, .1) do agents treat themselves ‘merely as a means to satisfy an animal impulse’ (6: 425.25–6), but that they also do so in any sexual act that is ‘natural’, yet by which the end of procreation cannot be served.Footnote ²⁶

Accordingly, in the casuistical question under consideration, the question is not whether non-procreative sex is something altogether morally indifferent. Rather, it is assumed that it is something ‘that is in itself not permitted’ (6: 426.14) and that would therefore require a special permissive law for it to be allowed. Moreover, the question is also not whether such a permissive law would allow non-procreative sex as such, but whether there is such a law that allows it ‘(indulgently, as it were) in order to prevent a still greater violation’ (6: 426.14–15).

One might argue that the subsequent text would speak in favour of reading Kant as taking a permissive stance on the matter of non-procreative sex. Following upon the question under consideration, the text continues thus:

Many interpreters read this further question in conjunction with the question under consideration, hence as also concerning the issue of non-procreative sex. Thus, Timmons, for instance, holds that ‘Kant poses only one question of casuistry in this article’ (Timmons Reference Timmons, Trampota, Sensen and Timmermann2013: 240; cf. also Reference Timmons2021: 165). Similarly, Gregor holds that the permissive law considered by Kant is meant to formulate ‘an exception to the imperfect duty of practising the virtue’ of chastity (Gregor Reference Gregor1963: 142). Mertens, in contrast, argues that Kant ‘seems to understand this collision of duties as one between a wide obligation towards the partner and a strict duty to self’ (Mertens Reference Mertens2014: 339).

In the passage just quoted, Kant seems clearly to adopt the view that one should not be overly pedantic as long as one is aware of the danger of slipping into violations of duty when giving in to sexual inclinations too much. However, I take the further question, just quoted, to be separate from the issue with which we are ultimately concerned. The further question (which in the text is separated from the question we are concerned with by a dash) deals with a ‘wide obligation’ (6: 426.16), and matters of latitude do not require permissive laws, which formulate exceptions to strict prohibitions (cf. Perpetual Peace, 8: 348 n.).Footnote ²⁷ In contrast, as the comparison with ‘unnatural lust’ (6: 426.11) shows, the casuistical question under consideration concerns the violation of a perfect duty, which is the topic of the section of the Doctrine of Virtue in which TL §7 is located (cf. 6: 421.5). The question, then, is whether agents violate their humanity by engaging in unpurposive sex, i.e. whether they violate a perfect duty to themselves.

While the question we are concerned with refers to the argument in the main part of TL §7 according to which even merely unpurposive sex is forbidden, the point of reference of the further question regarding the permissible extent of latitude is the virtue of chastity which is also mentioned in the main text of TL §7: whereas ‘[t]he vice engendered through [carnal lust] is called lewdness; the virtue with regard to this sensuous impulse is called chastity’ (6: 424.31–2). The question quoted above clearly deals with the issue of determining where the boundary between chastity and lewdness lies.Footnote ²⁸ But this is a distinct issue from the (either-or) question as to whether non-procreative sex is permissible or not.Footnote ²⁹

In the formulation of the casuistical question that we are concerned with, unpurposive, non-procreative sex is regarded as ‘in itself’ a violation of humanity in one’s own person (6: 426.14). (As we have seen, the ‘rational proof’ presented in the main part of TL §7 shows that also the ‘even merely unpurposive[] use of one’s sexual attribute’ is a violation of duty to oneself.) Could this transgression of duty be justified, in Kant’s view, by a permissive law on the grounds that this is necessary to avoid even greater violations of duty? As I have pointed out in the introduction, most interpreters hold this view. However, several reasons speak against this.Footnote ³⁰

First, the argument Kant offers for the purported permissive law assumes that sexual desire cannot be overcome but will necessarily lead agents to satisfy it one way or the other. Kant does indeed regard sexual desire as one of our strongest inclinations, and in one handwritten note he even regards our sexual drive as ‘insuperable’: ‘God thus based the most urgent end, one that allows for no respite, namely the maintenance of the species, on an insuperable drive’ (auf einen unüberwindlichen Trieb) (Refl. 7599, 19: 466.10–12; translation modified). However, Kant still believes that sexual desire can be overcome. This is evident from the gallows example in the second Critique (§6, 5: 30.22–35). There, Kant asks, first, whether someone who ‘asserts of his lustful inclination that, when the desired object and the opportunity are present, it is quite irresistible to him’ could overcome his desire ‘if a gallows were erected in front of the house where he finds this opportunity and he would be hanged on it immediately after gratifying his lust’. As Kant says, ‘[o]ne need not conjecture very long what he would reply’. Kant then poses the question whether the agent could also overcome his love of life ‘if his prince demanded, on pain of the same immediate execution, that he give false testimony against an honorable man whom the prince would like to destroy under a plausible pretext’. Kant is adamant that it is possible to take the moral course of action even if it means that one will suffer death because of it.

The gallows case thus shows that, according to Kant, not only can our sexual desire be overcome by other inclinations, but all our desires can in principle be overcome if morality demands as much: ‘To satisfy the categorical command of morality is within everyone’s power at all times’ (5: 36.40–37.1). In line with this, Kant in the Metaphysics of Morals Vigilantius explicitly states that ‘[m]an can only be affected by the stimulus, never determined to action; as a free being, it is therefore also possible for him to omit all actions to which the impulse of nature attracts him, and which he would undertake as a man of nature’ (27: 494.20–23). (Thus, when Kant, in the handwritten note quoted above, speaks of sexual desire as being an insuperable drive, he apparently means that we cannot rid ourselves of it, not that we cannot overcome it in particular instances.)

Secondly, Kant, in the Introduction of the Doctrine of Virtue, emphasises that ethical requirements are not subject to empirical factors:

Moral standards are not shaped by our abilities. On the contrary, the moral law makes us aware of our freedom from being determined by sensual inclinations. Indeed, we know our freedom ‘only through the moral imperative’ (MS, Division I, 6: 239.16–18). Kant thus retains his earlier view in the Metaphysics of Morals. This means that in the cases mentioned in TL §7, agents are not faced with a dilemma between non-procreative marital sexual intercourse, which is inadmissible in itself, on the one hand, and ‘contrapurposive’ sexual acts (i.e. masturbation) or unrightful intercourse (i.e. adultery) on the other. According to Kant, there is always the option of completely refraining from satisfying one’s inclinations. As Kant says in the second gallows case: ‘He would perhaps not venture to assert whether he would do it or not, but he must admit without hesitation that it would be possible for him’ (KpV §6, 5: 30.30–33).Footnote ³¹

Finally, Kant in the second Critique explicitly warns against ‘degrad[ing] the moral law from its holiness by making it out to be lenient (indulgent) and thus conformed to our convenience’ (5: 122.31–3). This, too, speaks against the presumption that Kant would think that there is a permissive law that would ‘indulgently, as it were’ (TL §7, 6: 426.15) allow an action that is, as we have seen, in itself not permitted.