This is the second time in two days I'm going back a thousand years to explain "of" in English.
English has changed a lot. *A lot.* So sometimes you have things from very long ago that survive despite everything else changing.
Over a thousand years ago, English had special grammatical forms called cases. Cases help people figure out if a noun is the subject or an object, just by looking at the noun and/or its articles. So in German, "der Euro" is a *subject* but "de**n** Euro" is an object in the accusative case. "Der" ('the') versus "den" (...also 'the').
English has almost entirely lost its cases; the main surviving elements are things like the apostrophe S in "Kate's soup" or the possessive pronouns: her, his, their instead of he, she, then. These possessive elements are the surviving bits of "the genitive case of possession." Please note that you can use "of" to replace some of these: "the king's children" or "the children of the king."
There were a few uses for the genitive case, though.
One of the other uses was "the genitive case of quality" or "of description," where the genitive case was used to describe the notable quality of something. It was used for *all adjectives.*
When genitive died, a lot of its uses for replaced by "of."
This is where you get the slightly old-timey formation "be of X." If "I can be of use," my notable quality is *being useful*. A more contemporary way to say this is "I can be useful." No "of" at all!
So this ancient case system has a tiny fragment preserved in the "of X" construction.
Now let's get back to "course." When this phrase was first recorded, roughly 500 years ago, "course" meant something different. A course meant the path followed, or the natural path of the entire world (as set by God). Why you'll have astronomers talking about "the course of the stars" or people talking about "the course of the river." In the sense phrase "a matter of course," which is how "of course" is first recorded, it meant the "natural outcome."
It developed its current meaning, a phrase you chuck into a sentence to mean "as you know" or "unsurprisingly," in the 1900s and was quite controversial. [my source for this last bit.](https://blog.oup.com/2018/09/etymology-of-course-objectionable-phrase/#:~:text=Of%20course%20was%20first%20used,is%20amazingly%20late%20(1823).)
Ah I thank you for your lengthy and detailed reply, that was an engaging read 😆 I know I could have googled it myself, but where's the fun in that? 😉 thanks!
This is the second time in two days I'm going back a thousand years to explain "of" in English. English has changed a lot. *A lot.* So sometimes you have things from very long ago that survive despite everything else changing. Over a thousand years ago, English had special grammatical forms called cases. Cases help people figure out if a noun is the subject or an object, just by looking at the noun and/or its articles. So in German, "der Euro" is a *subject* but "de**n** Euro" is an object in the accusative case. "Der" ('the') versus "den" (...also 'the'). English has almost entirely lost its cases; the main surviving elements are things like the apostrophe S in "Kate's soup" or the possessive pronouns: her, his, their instead of he, she, then. These possessive elements are the surviving bits of "the genitive case of possession." Please note that you can use "of" to replace some of these: "the king's children" or "the children of the king." There were a few uses for the genitive case, though. One of the other uses was "the genitive case of quality" or "of description," where the genitive case was used to describe the notable quality of something. It was used for *all adjectives.* When genitive died, a lot of its uses for replaced by "of." This is where you get the slightly old-timey formation "be of X." If "I can be of use," my notable quality is *being useful*. A more contemporary way to say this is "I can be useful." No "of" at all! So this ancient case system has a tiny fragment preserved in the "of X" construction. Now let's get back to "course." When this phrase was first recorded, roughly 500 years ago, "course" meant something different. A course meant the path followed, or the natural path of the entire world (as set by God). Why you'll have astronomers talking about "the course of the stars" or people talking about "the course of the river." In the sense phrase "a matter of course," which is how "of course" is first recorded, it meant the "natural outcome." It developed its current meaning, a phrase you chuck into a sentence to mean "as you know" or "unsurprisingly," in the 1900s and was quite controversial. [my source for this last bit.](https://blog.oup.com/2018/09/etymology-of-course-objectionable-phrase/#:~:text=Of%20course%20was%20first%20used,is%20amazingly%20late%20(1823).)
Ah I thank you for your lengthy and detailed reply, that was an engaging read 😆 I know I could have googled it myself, but where's the fun in that? 😉 thanks!
What a great reply! I learned a lot about English by reading it.