(Ok this is gonna be weird but a cursory look doesn't turn up any credible sources.)

I'm asking because of my previous question: According to Catholicism, can "co-parents-in-law" marry?

I assumed that step-siblings could not marry in Catholicism (or otherwise).

Based on this assumption, I questioned the difference between step-siblings' becoming a married couple and a married couple's becoming step-siblings.

Actually, apparently, step-siblings can even marry in other denominations and religions and even in civil law apparently. (Note: In the original question that my previous was based on, I wasn't able to see anything in the answers that even say 'Oh actually step-siblings may marry.')

Question: So, can step-siblings marry in Catholicism?

  • If yes: then oh Hell insane but whatever.

  • If no: then ok then back to the other question. (I didn't really analyse the answer and comments so thoroughly because I wanna double check this assumption 1st.)

Edit to clarify based on Andrew Leach's comment:

I mean suppose Alice and Bob are widows (or single adoptive parents or unmarried biological parents or whatever) and their respective children are Charlie and Dalia. And then Alice and Bob get married. The question then here is about Charlie and Dalia.

I'm not talking about cases like say Adam and Barbara have a biological child Carl and then later Adam and Barbara adopt Danielle, where I'd ask about Carl and Danielle. Or simply Adam and Barbara adopt 2 children. So not that. I mean to ask about the situation above with Charlie and Dalia.

  • 1
    You could perhaps make it clear whether you are asking about step-siblings who have or have not been adopted by the step-parent (I guess the question is about those who have not been adopted). Commented Jul 27, 2022 at 7:12
  • @AndrewLeach Ah like if Alice and Bob have a biological child Charlie and then later Alice and Bob adopt Danielle, then Danielle may not marry Charlie?
    – BCLC
    Commented Aug 11, 2022 at 13:33
  • 1
    Just so -- well I had thought of a situation where A brings C to the marriage, and B brings D; A and C marry; A adopts D and B adopts C. In English law, a marriage between D and C would not be lawful (void ab initio) because adoption effectively creates blood ties. I have no idea whether canon law thinks the same. Commented Aug 11, 2022 at 13:38
  • @AndrewLeach right thanks i'll edit
    – BCLC
    Commented Nov 13, 2022 at 7:58

1 Answer 1


Q: Can step-siblings marry in Catholicism?

A: Yes

See my answer to the question you linked. Step-siblings share no affinity or consanguinity (assuming their relationship does not extend beyond that which is described simply by "step-siblings). Thus there is no impediment to their marriage on that account.

  • 'share no affinity or consanguinity' - can be 'do not necessarily share affinity or consanguinity' ? Thanks SupportiveDante!
    – BCLC
    Commented Jul 25, 2022 at 3:25
  • Wait which part exactly says step-siblings do not necessarily share affinity or consanguinity?
    – BCLC
    Commented Jul 25, 2022 at 10:44
  • 1
    "Affinity 'pertains to the wife and the blood relatives of her husband, or the husband and the blood relatives of his wife.'" A man (father in law to his son's wife) shares no affinity with his son's mother in law (blood mother of the son's wife)
    – user54757
    Commented Jul 25, 2022 at 16:21
  • 1
    As for your first comment. Yes I suppose "do not necessarily share" is a fine alternate phrasing. But if there's another relationship whereby they share some other relation, then they're not really just step-siblings.
    – user54757
    Commented Jul 25, 2022 at 16:22
  • No offense, but I think 'do not necessarily share' is exactly the phrase to use and not merely alternate phrasing. It's maybe or maybe not. There's no harm here. It's absence of evidence. You can't be wrong. In your case you're saying there is none. That's evidence of absence. Same as here not necessarily.
    – BCLC
    Commented Jul 26, 2022 at 11:16

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