Something called ‘Natural Law’ sets the ground rules for all Catholic teachings about sex. Natural Law means the only Catholic approved sex is vaginal intercourse that can lead to procreation, and only when it is between a married woman and man couple. Any other sex at all is prohibited as ‘unnatural’ and the Church usually says it is a mortal sin. Many people search their informed conscience and disagree with both teachings and sinfulness. The common use of ‘artificial’ contraception within most Catholic marriages in the developed world is just one example of this.
The Natural Law rules about sex for Catholics are truly ancient: mostly they come from St Thomas Aquinas (1225-74), and he got a lot of his ideas from ancient Greeks like Plato and Aristotle, around 1,500 years earlier, a few hundred years BC. Interesting fact: ancient Greek texts had just come to Christian Europe’s attention because they were rescued from oblivion by Islamic scholars.
Aquinas and his homosexual deception
Another little known fact – Aquinas cheated and bent what Aristotle said about innate, natural homosexual behaviour, to help justify his and the Church’s condemnation of all homosexual behaviour. Aquinas, instead of talking of innate behaviour, said homosexual behaviour was something people acquired which then becomes ‘second nature’ to them – in other words Aquinas made it something people choose, instead of being born with. A choice is deliberate, so his twisting of Aristotle’s facts and reasoning helped the Church to call homosexual behaviour a deliberate sin, and Aquinas made it the particularly grave sin of ‘unnatural vice’. We’ll examine exactly how Aquinas performed this deception trick in Part Four of this series of posts on Natural Law.

Challenges to Natural Law: cracks in the dam
It is no surprise that something so ancient and so strict about how humans may sexually express our love is being seriously challenged in the 21st century. The Natural Law dam that is Catholic sex teaching is showing some serious cracks. Because Catholic Natural Law bans any lesbian and gay sexual expression, lesbians and gay men in particular have been asking tough questions about how sound the Church’s teaching really is. Many of us are not convinced at all by the Church’s wobbly defence of its Natural Law basis. Heterosexual women and men too have disputed the contraception ban especially, since the 1960s. Altogether there’s very many frustrated and unhappy Catholics who are urging a major sexual morality rethink, including expert Catholic moral theologians and ethicists. Outside the Church, even secular natural law theorists are struggling to hold the creaking Natural Law sexual morality edifice in one piece. It’s past its sell-by date.
Natural Law explored and tested : Part One of Four
This is the first of four posts, and the series will investigate the strange and unfamiliar world of Catholic Natural Law. We’ll find out why its rules about sex are so strict. We’ll reveal its male viewpoint and discover that significant things about women’s bodies, needs and ideas are simply ignored by the Church. All kinds of experts and thinkers have been turning inside out the Catholic teachings on sex and Natural Law, and very few are convinced by what they find. Catholic teaching on sex and relationships is a mess and a lot of senior people now realise this. Changing the Church’s sexual teaching is inevitable, but won’t come easily or quickly. But there are signs that change is on its way.
Catholic moral theologians’ ideas explored
This ‘Natural law’ and sex series ties in with posts from Terence about Catholic moral theologians discussing lesbian and gay sexuality. We’ve heard about the ideas of:
Dr James B Nickoloff, is an openly gay Catholic theologian who tells it straight. It’s not lesbians and gay men who are ‘intrinsically disordered’ but Catholic sexual teaching on lesbian and gay relationships. He tells us his idea of what the path ahead looks like for lesbians and gay men in the Church.
Bishop Geoffrey Robinson tells us the teaching for heterosexuals must change before it can change for lesbian and gay people. He wants the Church to shift the sexual rules from an obsession with sex acts, to focusing on the people, relationships and doing no harm.
James Alison is a priest and theologian who is openly gay and keen to help the Church get out of its rut of inexcusably blaming lesbians and gay men.
There are also heterosexual Catholic ethicists writing on similar themes: Todd Salzmann and Michael Lawler, who wrote ‘The Sexual Person: Toward a Renewed Catholic Anthropology’, and
Sister Margaret Farley, author of ‘Just Love: a Framework for Christian Sexual Ethics’, among other moral ethicists.

‘Disordered’, wrong teachings, in need of significant review
Each of these experts in their own way have criticised the Church’s teaching on sexual morality as ‘disordered’, wrong, and badly in need of thorough updating and review, for everyone, heterosexuals and lesbians and gay men.
Aquinas: ‘Doctor of the Church’
The Natural Law and theological influence of St Thomas Aquinas, who is a ‘Doctor of the Church’, gives his ancient work particular authority in the Church canon and tradition. His contribution and the high esteem in which he is held by the Church is a major reason why it is especially slow and reluctant to review and change traditional teaching and interpretations of scripture on sexual morals. You have to be pretty brave to say St Thomas got things wrong, when he has a title of distinction for getting theology right. But that’s what more and more experts, and lay people, are doing.
Every time the Pope or Bishops talk about lesbian and gay sexuality and gay marriage as ‘unnatural’ or ‘intrinsically disordered’ in Pastoral letters, Vatican documents and the Catechism, that’s a reference to Natural Law. Why is most contraception called ‘artificial’ contraception by the Church (no doctors use that phrase)? That’s because using contraception is ‘unnatural’ according to the Church, it’s against Natural Law, because it blocks natural procreation.
Natural Law

Natural law is deductive, based on the idea that everything in the world has its own natural purpose, and that we can work out the purpose of things through observing, reasoning and deducing things, like a detective. Thomas for example says, about the sex that is permissible:
Wherefore it is no sin if one, by the dictate of reason, makes use of certain things in a fitting manner and order for the end to which they are adapted, provided this end be something truly good.
Natural law deduces that fulfilling the proper natural purpose of our human design is the only ‘good’ use of our human faculties, and any misuse, contrary to their natural purpose, will be against natural law. Noses are for breathing and smelling things like roses, not for snorting cocaine.
So our moral rules are derived from the nature of the world and the nature of human beings. Since humans are by nature rational beings, we should behave in ways that conform to our sensible, rational nature. Thus, Aquinas and the Church derive natural law and moral rules from the inherent nature of human beings.
Homosexuality in nature
However defenders of orthodox interpretations of Natural Law insist that it does not mean everything “as found in nature”. So the same sex behaviour that is widely seen in all kinds of creatures in the natural world is not proof that this is natural for some humans too. Some even contend that ‘homosexuality in animals is a myth’, such as the conservative Dr Antonio Pardo, a Spanish professor of Bioethics. He argues that there is no such thing as homosexual behaviour in nature, and while some animal behaviours just look homosexual, these can all be explained by dominance and the strong sexual urge. Few bioethicists who’ve studied the phenomenon share his opinion.

His contention that all animal same sex behaviour is explained by dominance and the sex urge, simply disregards the breadth and depth of the available zoological evidence and the diversity of reasons why different creatures engage in a huge variety of non-procreative sexual behaviours, and why same sex animal couples raise young. Only some of the animal diversity of sexual exuberance can be characterised as homosexual, and ‘dominance’ is clearly not the real explanation. See this detailed, illustrated discussion, by Terence last week.
Another favourite dismissive argument is that (to use human behaviour labels) incest, cannibalism and rape are also found among animals, and those are immoral for humans and so too must be all homosexual behaviour. That’s a weak argument because it ignores the reality of the very specific all-encompassing Catholic prohibition on all sex, including among heterosexuals, which is not strictly marital vaginal penetration open to procreation. However we know very many human societies, including historial and current Christian societies, have or had no such taboos on other heterosexual behaviours, and some human societies find no problem in homosexual expression. Most people can see a clear category difference between causing harm to others (rape, cannibalism), and taking irrational risks of genetic abnormalities appearing in the longer term (incest), and the mutual loving of chosen life partners (homosexuality).
Arguing humans can only enjoy a one dish sexual menu (marital vaginal penetration for procreation only) because that is all that can be justified from the evidence of nature and ‘right reason’ is just bizarre. Different human societies in different places and times have their individual sexual moral codes of behaviour, all much more varied. These are all part of natural human social diversity. Attempting to exclude homosexual expression as uniquely transgressive for all humans makes no logical sense. Even Aristotle did not exclude homosexual expression as unnatural in law.

This bar on homosexual expression and all heterosexual sexual activity that is not marital vaginal penetration for procreation, is all the creation of Aquinas and his successors, using reasoning that is directed to a series of ends found by reference to pre-existing misinterpretations of Old and New Testament scripture and of Church tradition.
The evidence was selected, sometimes twisted from Aristotle’s original, and Thomas’s reasoning happened to suit particular and preferred Catholic conclusions.
English translations of Thomas’s writings on sex
First in these translations of Aquinas is what he has to say on ‘unnatural vice‘; this is much broader than simply lesbian and gay sexual expression, and includes heterosexual sex that is “not observing the natural manner of copulation, either as to undue means, or as to other monstrous and bestial manners of copulation,” and masturbation and bestiality. These are all grave sins in Aquinas’s mind. Few people these days can accept that masturbation is in the gravest category of sins. If that’s OK, what does that mean for the rest on Aquinas’s grave list?
The key passage dealing with lesbian and gay sex, masturbation, bestiality and unnatural heterosexual sex is this:
As stated above (A6,9) wherever there occurs a special kind of deformity whereby the venereal act is rendered unbecoming, there is a determinate species of lust. This may occur in two ways: First, through being contrary to right reason, and this is common to all lustful vices; secondly, because, in addition, it is contrary to the natural order of the venereal act as becoming to the human race: and this is called “the unnatural vice.” This may happen in several ways. First, by procuring pollution, without any copulation, for the sake of venereal pleasure: this pertains to the sin of “uncleanness” which some call “effeminacy.”[=masturbation] Secondly, by copulation with a thing of undue species, and this is called “bestiality.” Thirdly, by copulation with an undue sex, male with male, or female with female, as the Apostle states (Rm. 1:27): and this is called the “vice of sodomy.” Fourthly, by not observing the natural manner of copulation, either as to undue means, or as to other monstrous and bestial manners of copulation. [=non-procreative heterosexual sex acts]
The second is about sex in general, including fornication, incest, adultery, rape etc.
The key passage about permissible heterosexual sex is here:
I answer that: A sin, in human acts, is that which is against the order of reason. Now the order of reason consists in its ordering everything to its end in a fitting manner. Wherefore it is no sin if one, by the dictate of reason, makes use of certain things in a fitting manner and order for the end to which they are adapted, provided this end be something truly good. Now just as the preservation of the bodily nature of one individual is a true good, so, too, is the preservation of the nature of the human species a very great good. And just as the use of food is directed to the preservation of life in the individual, so is the use of venereal acts directed to the preservation of the whole human race. Hence Augustine says (De Bono Conjug. xvi): “What food is to a man’s well being, such is sexual intercourse to the welfare of the whole human race.” Wherefore just as the use of food can be without sin, if it be taken in due manner and order, as required for the welfare of the body, so also the use of venereal acts can be without sin, provided they be performed in due manner and order, in keeping with the end of human procreation. [= vaginal penetration open to fertilisation]

Ancient Greek misreadings of nature
Scholars like James Boswell and other academics clearly trace Aquinas’s ideas back to Aristotle’s own misreadings of the sexual behaviour of animals. Other scholars point to Aquinas’s misrepresentation of Aristotle’s findings on human homosexual expression.
Ignorance of evolution and the female perspective
The ancient Greek roots of Natural Law and Aquinas’s contributions in the 13th century mean none of them knew anything about the processes of evolution which influence sexual behaviour throughout nature, and they also all saw things solely from a male perspective. We’ll come back to their ignorance of evolution and the male-only perspective later, because these are the origin of some big cracks in the natural law moral dam.
Aquinas, Creation and God
While Aristotle didn’t believe in any creation by a god (he believed the world had always existed) and simply used reasoning from observation of nature and form to deduce everything’s purpose, Aquinas believed in God’s creation. For Thomas the creator God was involved in designing the natural purpose of all things and the Bible helped him decide that natural purpose. So Catholic Natural Law is an odd mixture of nature’s supposed purposes, with the addition of Bible and God, whenever Aquinas needed to import these to buttress a version of Natural Law to suit him and the Church.
Body Parts decide the natural law of human sexuality
In considering human sexuality, the starting point is the purpose of various body parts. The purpose of eyes is to see, and you can deduce this from close examination of their parts and connections to the brain. The purpose of lungs is to breathe air and so oxygenate the blood and then expel waste carbon dioxide.
In this natural purpose design view, the penis has a dual purpose, excretion and procreation. In procreation it is designed to penetrate the vagina and deposit semen, in order to fertilise a woman’s egg.

Any other usage of the lungs than to breathe would be unnatural and irrational, and therefore morally wrong, as this is not part of God’s creation design for the lungs. Using the lungs to sniff glue to get high, or to smoke, or depriving the lungs of fresh air for the risky thrill of asphixiation, are neither natural nor rational, not part of their design purpose.
By the same token, using the penis purely for pleasure as in masturbation, or for penetration of other orifices, as in oral or anal sex is, in the Church’s strict conception of the natural purpose of things, neither natural nor rational. The Church teaches that natural and rational sexual faculty use is strictly intended by God only for procreation. Church teaching that limits sex to procreative vaginal sex within a married couple is tradition and scripture-based, with a Natural Law cloak of simplistic use of interlocking body parts. It wilfully ignores widespread natural human and animal sexual behaviours that are clearly not for procreation. It ignores Aristotle’s uncritical words about the sexual activities of innately homosexual men.

God and the Bible imported into natural law
Although it is called natural law, because God was the creator / designer of everything, Aquinas and the Church often import God and the Bible into nature to buttress their natural sexual morality conclusions, to justify excluding some uses of our sexual faculties which they designate as ‘unnatural’. It would be more honest for the Church to say unprocreative non-marital uses are un-Godly or un-Biblical, rather than un-Natural, against ‘natural law’. The fusion and confusion of natural and doctrinal, makes challenging the Church’s version of ‘natural law’ frustrating.
St Thomas Aquinas was in at least one key instance a naughty deceptive moral theologian, because he buried and distorted some key passages in Aristotle to suit the Church and his own anti-gay hostility, in order to render homosexual activity ‘unnatural’.
Slippery as eels
The deliberate blurring of the boundaries between what humans can reason solely from nature, and God’s presumed intentions for his human creation, makes the Church’s so-called ‘natural law’ limits on sexual behaviour problematic. God and interpretations of the Bible are imported to justify some behavioural rules that can’t be inferred by reason alone from observing nature and through pure reasoning to decide what would be ‘right conduct’. But the Church nonetheless calls this fusion ‘natural law’.

The Church does not use or recognise a 21st century scientific understanding of the natural world and evolution, but sticks with a Bible-infused 13th century conception of nature. This makes a rational discussion of sexual morality with the Church a problem, because ‘nature’ keeps shapeshifting between a quasi-scientific natural world view, and a theological, bible-based conception of the world of nature. In the middle of a piece of nature-based natural law, suddenly the Bible or God are produced out of a hat. The Aquinas model of natural law with added Bible and God means the Church sets the rules and so tries to win every argument, because whenever it is losing on nature grounds, it calls on its traditional interpretation of the bible and theology to rescue it.
What’s next in Part Two?
Next time, we will consider how the Church’s sexual teachings are distorted because they only look through male eyes.
We will carefully consider male and female sexual body parts which Aquinas and the Church ignore, and contemplate Natural Law through women’s eyes, for a really fresh perspective. It’s very satisfying seeing things differently.
More about Aquinas and Natural Law ethics
Natural Law and Homosexuality in the Stanford University Encyclopedia of Philosophy
Farley, Margaret. “Just Love: A Framework for Christian Sexual Ethics,” Continuum, 2006