Preface

There is no shortage of interest in 6th Commandment studies today, albeit those who do take up the task involve themselves in various risks. First, they risk teaching error about points of great moral weight with grave spiritual consequences. Second, they risk occasioning sin by frequently dwelling on items that easily lead to unchastity and drawing others to do the same. Third, they risk being labeled and derided in various ways and criticized without mercy for laxity or rigorism, even simultaneously. It is a task that few people are able to undertake wisely.

Mindful of all these considerations, relying on the help of God, this author has chosen to take the risk.

Another risk, already overcome, is to be convinced that with respect to true moral questions related to chastity there is already a binding consensus on all points of interest, that there is little left to say, and that anyone generally renowned for learning and orthodoxy – or even someone who simply has a big platform or a reputation as a “chastity guru” – surely has the right answer about “what the Church teaches” on the little that seems controversial. These opinions are foolish. Charismatic speakers with dramatic life stories that are closely related to the practice of chastity have their place, and that place is rhetoric; it is the keynote speech at the youth conference, the podcast interview, the “witness talk.”

Trusting someone like this to be a guide through the thornier questions related to marriage ethics is a bit like trusting an actor who survived a bad car accident because they were texting or drinking to give you advice on spark plug upgrades for your engine block – it makes no sense, as it does not correspond to their expertise, even though they know very well the importance of driving safely and can convey this better than almost anyone. Instead, even though it is more boring, if you want expert advice on spark plugs you should go to a mechanic.

I came into the study of the 6th Commandment somewhat by chance. It has never figured very large in my formal academic study at any point in my career. Rather, when choosing a theme for a paper I would write and present at a conference at my university in Rome (the Angelicum), I decided to investigate what St. Thomas Aquinas would think about “NFP.” (This explains some of the structure of the present text; were I to begin again from nothing, probably I would not begin Chapter One the way I do, for example.) After receiving high praise and much interest from peers on this topic subsequent to the presentation of the original paper, I endeavored to dig more deeply into the subject and found an entire world of complex questions and puzzles, many as yet unsolved. Given the great import of sexual ethics, it amazed me that there could be such disagreement among the classical authorities on so much related to chastity, and it dawned on me at some point that there had been very little serious extended moral examination of NFP in part due to the fact that there was no true scientific consensus about the mechanics of female fertility until the mid-1800’s. This text is the first attempt at such an examination in some time, perhaps since Dr. N. Orville Griese’s very helpful and interesting text printed in 1944, The Rhythm in Marriage and Christian Morality.

Griese’s text is a good guide through the early academic history of the question of NFP (then called by other names), such as the teaching of Cardinal Gousset, Fr. Lavaud, O.P., Fr. Salsman, S.J., and some of the major moralists of the time (especially Vermeersch and Merkelbach). He lays out a very rigorous position of his own, which largely tracks the teaching which will be presented here, though the book has its lacunae; these include a failure to engage seriously with the teaching of St. Thomas and St. Alphonsus on the use of conjugal acts, little discussion of the complexity of the controversy around Innocent XI’s doctrine, and a seeming lack of awareness of the 1932 responsum of the Sacred Penitentiary. The suspicion of motivations for couples who wish to use NFP – and in particular, the way clergy ought to treat the topic in counseling the faithful – is perhaps slightly too severe, and is at least unworkable today. However, I strongly recommend those especially interested in the pastoral work related to NFP to read his considerations with open minds.

The hope for this book is not only to begin (or restart) a serious conversation about the morality of NFP but also to inaugurate a renewal of the study of sexual ethics more generally. Deeper study in the controversy around Innocent XI’s condemnation of solam voluptatem would be particularly helpful, as would be a full translation and reprinting of Sánchez’s magnum opus on marriage. Studies in Gratian and the treatment of marriage in early to late medieval canon law would also potentially be fruitful – I decided to remove from the text the little content on this that I had written, as this dimension of the discussion deserves a kind of treatment which I cannot at this time undertake properly.

In my research I came upon some rather obscure authors with helpful opinions somewhat by chance – much more swimming in the ocean of older manuals is warranted. There are doubtless many more treasures to find in long forgotten ships, sunk in the deep waters of centuries past.

The reader is asked to consider the arguments carefully and with the understanding that much more could and should be said. This is only the beginning of the work. The author is aware of the immense interest in this topic and no doubt the immense attention which this text will receive, and he apologizes in advance for the errors which he has no doubt made and for his lack of clarity in exposition in his sincere effort to understand and to promote the fullness of chastity among married couples.

I wish to thank my professors and all the friends with whom I have had conversations about the content of this book over the past few years and who have been encouraging in its writing and the broader project to which it is attached. Particular mention must be made of Christian B. Wagner, Thomas Mirus, Michael DeMarco, and Louis Knuffke. I also thank Anne Stephens for her assistance in transcribing and translating the text from Fr. Steinhuber which I cite and will publicly present in some time in connection with this work.

I have provided this material free of charge, for those who cannot afford to pay. I humbly ask those who can manage it to make a donation by scanning the QR code or following the link found in the frontmatter and backmatter of the text. Even if you ultimately do not find my arguments convincing, hopefully you can appreciate that you have been provided with what will certainly become the text of reference for the serious moral discussion on NFP moving forward through the dedication and risk of a mere Roman doctoral student with meager temporal resources.

-Eamonn Clark, STL
Albano Laziale, Rome, Italy
July 17, 2025