So I should point out that grammatically there has never been a plural form of philosophy, until quite recently. Philosophia cannot be plural in attic Greek, its origin, as the love of wisdom always already embodied the goddess of wisdom; Sophia. Sophia cannot be plural, i.e., there is only one Sophia.

This carried over into Latin as well, and even as philosophy was divorced from the belief in the goddess per se, the idea that wisdom is "one" remained well into the rise of Existentialism. As early as the late 90's/turn of the Century, most spell checks would not allow for the term philosophies, it would be flagged as misspelled; something I see the spell check here does not do. There ya have it. Still, what happened? When did the goddess get torn asunder?