Ethnicity vs. Religion: Why Some Groups Are Both at Once

Religion is a system of belief and practice you can adopt or abandon. Ethnicity is a form of group membership grounded in a belief in shared descent. One is, in principle, open to anyone. The other is inherited, and access to it is controlled by the group.

Most cases are easy. Catholicism is a religion, not an ethnicity — Catholics are Filipino, Irish, Brazilian, Congolese. Yoruba is an ethnicity, not a religion — Yoruba people are Muslim, Christian, and practitioners of traditional Yoruba religion in large numbers.

The interesting cases are the ones where the two have fused so completely that separating them distorts what is actually there.

The asymmetry that explains everything

Here is the cleanest way to hold the distinction.

You can convert into a religion. You cannot unilaterally convert into an ethnicity.

Every major world religion has a mechanism for admitting outsiders — baptism, the shahada, taking refuge. That openness is often central to the faith’s self-understanding, since a universal truth claim implies universal access.

Ethnic groups have no equivalent. There is no ceremony that makes an outsider Kurdish or Japanese or Zulu. Membership comes through descent, and where boundaries can be crossed at all, it happens slowly across generations through intermarriage and assimilation, and always subject to recognition by the existing group. You do not admit yourself.

This is why the question “can I claim this identity?” has a straightforward answer for religion and a complicated one for ethnicity.

Ethnoreligious groups: where the categories fuse

Some communities are genuinely both, and the fusion is a historical fact rather than a category error.

Jewish identity is the most discussed case, and the numbers make the point plainly. Pew’s 2020 survey of Jewish Americans found that 27% are “Jews of no religion” — people who describe themselves as atheist, agnostic, or nothing in particular, but who had a Jewish parent or were raised Jewish and still consider themselves Jewish ethnically, culturally, or by family background. The remaining 73% are Jewish by religion. A quarter of the population holds the identity with the religious component removed entirely, and no one regards this as a contradiction.

Test the symmetry: a “Catholic of no religion” is not a coherent category. A Jew of no religion is a category Pew can survey.

Sikh identity works similarly in law, if not in theology. Sikhism is a revealed religion with a scripture and a conversion path, yet UK courts classify Sikhs as an ethnic group — more on that below.

Druze, Yazidi, and Parsi communities take the fusion further still. All three are effectively closed: the Druze have not accepted converts since the eleventh century, Yazidi identity passes only through birth to two Yazidi parents, and Parsi communities have historically not admitted outsiders. For these groups, religion and descent are not merely correlated — the faith is defined as belonging to the people. There is no way to be one without being the other.

What courts decided

Anti-discrimination law has had to resolve this, because a defendant who says “I discriminated on religion, not race” is claiming a different legal regime.

Mandla v. Dowell Lee (UK, 1983). A Sikh boy was refused a school place over his turban. The Court of Appeal held that Sikhs were a religious group and so outside the Race Relations Act’s protection of racial and ethnic groups. The House of Lords reversed. Lord Fraser’s test required a long shared history the group is conscious of, and a distinct cultural tradition — and listed “a common religion different from that of neighbouring groups” as one of several supporting characteristics. Religion was an ingredient of ethnicity, not an alternative to it. Sikhs were an ethnic group.

Shaare Tefila Congregation v. Cobb (US, 1987). A synagogue in Maryland was defaced with antisemitic slogans and symbols. The congregation sued under § 1982, the Reconstruction-era statute barring racial discrimination in property rights. Lower courts held that Jews are Caucasian, so no racial discrimination had occurred. The Supreme Court reversed unanimously, on the same day it decided Saint Francis College v. Al-Khazraji: what mattered was whether the group was regarded as a distinct race when the statute was passed in 1866, and Jews clearly were. The claim could proceed.

Both rulings land in the same place. Where a community is targeted as a people rather than as believers, the law treats it as an ethnic case regardless of the religious label — because that is how the discrimination actually operated.

Where religion creates ethnicity

The relationship also runs the other way. Religious difference, sustained long enough, can manufacture an ethnic boundary where none existed.

The clearest example is the former Yugoslavia. Bosniaks, Croats and Serbs share a common South Slavic descent and speak what linguists treat as one pluricentric language. The historical dividing line is confessional — Muslim, Catholic, Orthodox — inherited from Ottoman and Habsburg rule. Over centuries, that religious boundary hardened into separate scripts, separate national narratives, separate ethnic identities, and eventually into war between populations that were, by descent, the same people.

This is Fredrik Barth’s argument made concrete: the boundary is what constitutes the group, and religion is simply one of the more durable materials a boundary can be built from.

Northern Ireland shows the same mechanism in a milder form. “Catholic” and “Protestant” there function as ethnic labels attached to communities distinguished by settlement history and political allegiance — which is why the terms still apply to people who never attend a service.

Quick comparison

	Religion	Ethnicity
Acquired by	Birth or conversion	Descent
Can you join?	Yes, by a defined process	Not unilaterally
Can you leave?	Yes — apostasy, disaffiliation	Not cleanly; often persists regardless
Requires belief?	Generally yes	No
Central claim	Something is true	We share an origin
Overlap cases	Jewish, Sikh, Druze, Yazidi, Parsi	Jewish, Sikh, Druze, Yazidi, Parsi

The row that does the most work is the third. Leaving a faith is a recognised act with a name. Leaving an ethnicity mostly isn’t — a secular Jew is still Jewish, a non-observant Sikh is still Sikh, and someone who wants to exit an ethnic identity typically finds that others keep applying it.

And what a photo can’t tell you

None of this is legible in a face. Religion leaves no phenotypic trace whatsoever, and ethnoreligious identity — the fusion of descent and faith — is precisely the kind of social fact no image contains.

An AI ethnicity detector reads facial features and returns population-level associations. It has no access to what you believe, what community claims you, or which of the two you would name first if asked who you are. Useful as a prompt for research; not an account of your identity.