On the Metaphysics of Nations -- Chapter 2, Section VII
The Ethnic Group -- The Metaphysics of Multi-Ethnic Individuals
The metaphysics of so-called "multi-ethnic" people is a topic of importance for me. If someone has a mixed heritage, what then? As the ethnic group is the fundamental level of human existence, an individual cannot fully participate in both/all heritage groups.
They fundamentally belong to one of the ethnic groups (usually the speech ways they participate in most comfortably reveal which group this is). However, the individual may incorporate background from the other ethnic group. This adoption of background is similar in both the individual and on the scale of the tradition of an ethnic group as a whole — the adoption of pseudo-foreign folkways may be aesthetic or indeed genuine but the adopted background folkways are likely to be compatible and contextualized within the geist of the fundamental ethnic group.

Other members of the ethnic group may or may not recognize the background of the "multi-ethnic" member of their ethnic group, though likely in a different category compared to how they would recognize a true member of the foreign ethnic group within their "in-group/out-group" distinction. In other words, an American may see a fully assimilated American of Japanese heritage with no connection to Japanese culture as an American (in-group), a Japanese-American with connections to Japanese culture but speaks English natively as an American with Japanese background (in-group "with eccentricities"), and a first generation Japanese immigrant who speaks English with an accent as a Japanese person (out-group).
The more "backgrounds" a "multi-ethnic" individual participates in, the more distinctions become unclear and they either lose traditional attachment1 (a trend seen among such individuals in the 21st century) or alternatively, the geist becomes more clear without clear externals (which was more common for such individuals in a pre-Enlightenment context).
Let us take a moment to review different applications of background for clarification.
Situation 1 — Background as Civilizational Heritage
Example: An Englishman (perhaps a clergy) praying in Latin. Latin, as the language of the Roman Empire, is part of the background of traditional English culture despite the Latin language not being part of an indigenous package within the English folkways. The Englishman here is still showing traditional attachment.

Situation 2 — Background as Ethnogenesis Heritage
Example: An Englishman creating an illuminated manuscript with Celtic knotwork and art styles. In the ethnogenesis and early history of the Anglo-Saxons, many insular Celtic artistic methods were readapted into Anglo-Saxon art forms. Despite the folkway coming from the Britonnic Celts, the Englishman here is still showing traditional attachment as the traditional folkway of another people became part of the tradition of his own people.
Situation 3 — Background as Multi-Ethnic Heritage
Example: An Englishman with a Japanese grandfather styles his garden with traditional Japanese aesthetics and philosophy. Despite being immersed in the folkway of another people, this particular Englishman is engaged in traditional attachment by participating in the folkways of his heritage. An Englishman without such Japanese heritage would be engaged in traditional attachment through such practice (though this is not inherently a bad thing so long as the Englishman is balanced in his life holistically).
Guénon defined "traditional attachment" as a state of being based on traditional principles as opposed to dissident doctrines. An individual is in a state of traditional attachment (and thus in-line with the Logos) when they are participating in the tradition proper to them. Do not misunderstand this as saying that it is not good to enjoy or experience other cultures beyond one's own. But to have no traditional attachment but to be either immersed in other cultures one does not belong/have a background in or to see oneself as "above" all cultures altogether results in cosmopolitanism, feeding into the individualized, rootless, atheistic, and materialist life that can become void of moral and virtue and without a guiding star to show you the way.