“Dogmas” is the ordinary English plural of “dogma,” while the classical plural “dogmata” is also recorded. The choice is therefore a genuine competing-plural question rather than a simple spelling variant.
Both “foci” and “focuses” are accepted plurals of “focus.” Do not assume the Latin-derived “foci” makes “focuses” incorrect; dictionaries record both forms.
Both “formulas” and “formulae” are accepted plurals of “formula.” Do not present “formulae” as the only correct plural or treat “formulas” as an error: both are dictionary-recorded forms.
“Forum” has two dictionary-recorded plurals: “forums” and “fora.” The regular plural is common in general use, while the Latin-derived plural survives especially in more formal or specialized contexts.
Cambridge records two plurals of “referendum”: regular “referendums” and formal “referenda.” The page keeps both forms valid and treats register/style as the choice factor.
