I already understand and so ask NOT about the definition, below which I want to burrow. I heed the Etymological Fallacy. 1. Which ODO definition corresponds? What does of mean here?

to be of = Possess intrinsically; give rise to

2. How does the juxtaposition of be + of effect/imply/induce this meaning?

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    Are you asking why this work is of interest, is the same thing as saying this work is interesting? The honest answer is that I don't know. But then I don't know why we use many idiomatic forms.
    – WS2
    Commented Oct 31, 2014 at 8:10
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    Do you mean as in "be of good cheer" and the like?
    – Robusto
    Commented Nov 1, 2014 at 1:27
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    "A general answer" is impossible when you ask about an idiom, for by definition the meaning of an idiom cannot be derived from its parts. Commented Feb 11, 2015 at 23:51
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    You can't derive an idiom's meaning from its parts, but in many cases you can explain the right way of looking at it so the meaning seems reasonable, and you can distinguish more and less reasonable ways of varying or extending it.
    – Ben Kovitz
    Commented Feb 12, 2015 at 0:14
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    @BenKovitz Thank you effusively again. Not only will I revisit your answer, but will also paraphrase your comment above on how to interpret idioms whenever I question etymology in the future!
    – user50720
    Commented Mar 15, 2015 at 3:35

2 Answers 2


In its oldest senses, of meant something like “away from”, which of has lost but is preserved in off (“come off the porch”, “what a rip-off!”). It comes from the same Indo-European root as the Latin word ab, which roughly means from or “the source of”.

The general meaning of indicating where something came from, or coming away from something, is still roughly preserved in most of the modern senses of of: indicating the source or origin of something (cuisine of Russia), a reference point for something else (north of Boston), the characteristic period of time when something happens or exists (the Rite of Spring, flowers of summer), something that is removed (cured of the hiccoughs, deprived of liberty), the cause of something (proud of his accomplishments, sick of eating rice), the result of something (a doer of good deeds, the wages of sin, the product of effort), and many more, including the senses probably most relevant to your question: material (made of mahogany), belonging or possession (territories of the United Kingdom), and properties or qualities (the speed of the wind, hair of red). These latter senses indicate something about the object which explains behavior. If you imagine that the quality that the object is “possessed of” exists deep within the object, and its behavior is more superficial or external, you might have found the right way to see various other senses as extensions of the primary one.


  • to be of foul temperament = to hold, deep within oneself, a foul temperament, which could give rise to foul behavior; similarly, to be of good cheer.

  • to be of age = to have reached a certain age, with the emphasis on the inner qualities that normally attend having reached that age.

  • to be of Russian descent = to have an ancestral origin in Russia.

  • to be of use = to be useful; to be among the useful, “of” the category of useful objects or people.

  • to be of the opinion that … = to hold that opinion; to be among the kind of person who holds that opinion; to have many other, consequential opinions that flow from the deeper opinion explicitly stated; to have come to that opinion from many experiences; for you, that opinion came out of much previous experience and thought.

  • Time is of the essence = An important aspect of the situation is that speedy action will be rewarded and dawdling will miss important opportunities. Of roughly indicates the source or inner nature; essence explicitly means what is most central or fundamental; so, to be “of the essence” means to be most definitely and unmistakably embedded in what is most central or fundamental.

I don’t think there is any one definition or sense of of that will uniquely explain these. Each can appeal to a different sense of of, to multiple senses simultaneously, or to the vague, general gist of it.

The word be just converts the prepositional phrase into a full predicate including a verb so you can use it where you need a verb:

A man of foul temperament was hired to manage my department today. So, as of today, my boss is of foul temperament.

  • this is nonsense: "In its oldest sense". The comparison to Latin gives some context to infer how old you mean, but that's neither the only old sense, nor the oldest. Just compare the richness of the po-*prefix in Slavic, nevermind that *u-, *Hew-, also epi, up, etc imply a richer etymology that that. Not to mention that German von ... sein parallels English, so this sense likely existed in Proto-West-Germanic, so that "of" in sensu strictu, as it appears in OE as the oldest form, already must have had this sense.
    – vectory
    Commented Apr 21, 2020 at 18:33
  • This is especially egregious when you cite "posess" (esse po(s)), that well matches the thought semantics and form!
    – vectory
    Commented Apr 21, 2020 at 18:37
  • @vectory It sounds like there is some misunderstanding, because I don't see much connection between your comment and the answer above. Maybe this is part of the misunderstanding: you quoted "in its oldest sense" and criticized the claim of a single oldest sense, but the answer says "in its oldest senses". Further clarification: I meant the oldest senses in English. These are presented in more detail in the OED, which also explains the emanation of senses from "away from".
    – Ben Kovitz
    Commented Apr 22, 2020 at 20:53
  • No, that's exactly what I'm criticizing, because if the same semantics exist in German, it's unlikely that this and that one arose independently in English and German respectively from a sense "away from"--which could only appear naturally convincing from the naive native speaker perspective, already familiar with the connotation, that henceforth does not explain anything.
    – vectory
    Commented Apr 22, 2020 at 21:28
  • @vectory Perhaps I'm misunderstanding. Do you mean that a word for "away from [an anchor]" couldn't possibly expand to this kind of variety of senses independently in multiple languages? Are you aware that the same happened with in Latin? It started as "down from [an anchor]" and expanded to become the all-purpose preposition in the Romance languages. I understand this to be a natural way for a preposition to "steal" the genitive case, hence something we should expect to see in many languages as their case systems weaken.
    – Ben Kovitz
    Commented Apr 24, 2020 at 21:36

Ben Kovitz has provided plenty of good examples, to which I might add the clear difference between "You are very kind" and "That's very kind of you."

The former is simply a statement of your general temperament, whereas the latter means you have chosen (from—of—many different possible ways to treat someone) to be kind to me instead of ignoring my plight or treating me with contempt. The second statement is considered 'polite' because I have recognized your choice and am grateful for it.

Another obvious example would be "You're stupid!" and "That was stupid of you!"

In the first sentence there is no hope for you; in the second you can return to your normal intelligent self in the future.

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