I know that "as to", "on", and "of" are synonymous with "about", but I also know these words are not always interchangeable. I was wondering if there are rules for picking between these prepositions.

  1. There is still no news as to whether he will leave the company. (all four can be used with no change in meaning)
  2. I don't know what you are talking about. (only about and of can be used)
  3. I heard of that from Jim. (only of and about)
  4. The speaker spoke on the issue of liquidity markets. (all four?)

Thanks for the help.

3 Answers 3


The most basic answer to your question is that when and how they can be used all comes down to their definitions. The words "of" and "on" have quite a few variations and so there is no single right way to use them, but several.

  • "As to" almost always points to a decision that needs to be made, is going to be made, or can be made. It seems to always be followed by an adverb, but I am not sure whether or not that is the rule.

    1. I am unsure as to how we will go about this. (how to go about this is what must be decided)
    2. As to whether or not you won, I could not say. (The winner has not been decided)
  • "On" usually indicates a detailed or direct relation between the subject and its modifying prepositional phrase. Think of it like an object sitting on a table - there is direct contact.

    1. He gave a speech on the ramifications of not wearing protective gear while cycling. (The ramifications were the main topic of the speech he gave.)
    2. She was working on a solution for the global climate crisis. (The global climate crisis was the main subject of her work.)
  • "Of" often lends itself to less knowledge or detail on a subject on the surface, though that is not always the case.

    1. I have heard of him before. (I have at least a general awareness of him, but don't necessarily know much more detail.)
    2. Of all the cars, twenty were red. (There were twenty red cars, but specifically which ones were is left uncertain.)
  • "About" simply signifies a relation or subject. It can indicate great detail or a general association. Often times "of" or "on" can be used in place of "about."

    1. He knew many things about life and love. (He knew a good number of things about life and love. It's very general. Both of and on can be used here.)
    2. Her story was about the joys of sailing. (The subject of her story was the joys of sailing. Both on and of can be used here, though I feel on would work better.)

Right, they aren't exact synonyms, and it's all pretty idiomatic.

So no hard-and-fast rules, no.

In 1, "news of whether" does not really work and would have to be reworded as "news of the possibility that" instead I would say.

In 4, "spoke of" has more of a meaning of "merely mentioned", whereas the others would mean closer to "spoke directly about". And "spoke to" would be less awkward than "spoke as to".

In general, "about" has a connotation of "directly but also around", where "on" means more "specifically to", and "of" requires a more definite object than the others. "As to" is a bit highfalutin as well.

  • So "of" is the weakest of the bunch, while "about" and "as to" are in the middle of the pack, and "on" is the strongest as in all the statements that make up speech said are on top of the topic in question. Also, in all instances of "as to", can I cut out the "as" without affecting the meaning of the sentence?
    – ed86
    Commented Dec 22, 2015 at 16:00
  • No, the "as" cannot usually be cut out, sentence 1 being an example. Only after certain verbs is "to" better than "as to". Again, it's idiomatic.
    – Jeff Y
    Commented Dec 22, 2015 at 16:56

In all of the examples, about can be used. Sentence #3 would sound better with about, while sentence #4 probably sounds better as written. Also, regarding sentence #3, if "I heard that from Jim" accurately conveys the meaning, it would be better than what is written.

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