If you take the sentence

"Bob will run or walk fast."

how is the ambiguity resolved between the following two meanings?

  1. Bob will either run fast or he will walk fast.
  2. Bob will either run (at some unspecified speed) or he will walk fast.

As this is such simple and common word usage I thought it would be relatively easy to find an answer to this online but I've had no luck.

I have seen this post dealing with the ambiguity of the word "or" but it only seems to be addressing how to recognize when or is used as a way of providing one or more synonyms for a word.

Edit: My question is whether a sentence that has more than one verb separated by one or more "ors" is always going to be ambiguous. If so, I'd imagine it should then be avoided in writing...so is there an alternative better than simply repeating the adverb (for meaning 1) or inserting a pronoun before the verb taking the pronoun (for meaning 2)?

5 Answers 5


Sentences of the form

Bob will run or walk fast.

are genuinely ambiguous: it is not explicit which is meant. You might guess from context that the most likely intepretation is "Bob will run or Bob will walk fast" but equally "Bob will call or email me when he arrives" is of identical form but the context indicates the reverse case.

The way the sentence is spoken (especially pauses) will usually give you an indication. In writing we can use punctuation to help disambiguate:

Bob will run, or walk fast.

= Bob will run or he will walk fast

Bob will run (or walk) fast.

= Bob will run or he will walk fast

However these clues are not always present, and it is not always easy to work out how to make the meaning clear.

Nor is the problem unique to or:

Bob will have dinner and sleep in the front room.

Is Bob eating in the front room, or just sleeping there?

In mathematics and in programming languages, there are often complex rules which define the order in which the parts of the statement are bundled up to ensure there is consistency (and hopefully, one which does what the user wants most of the time) - and when that fails, brackets can be used to override the rules. English does not have those rules for and and or and punctuation (or the spoken equivalent) can be used to disambiguate.


In speech, the intonation patterns and parsing rhythms of a native speaker would disambiguate one meaning from another.

Below I am trying to reflect a rising accent on the word run, a pause with the em dash, and words spoken in fairly rapid succession with "walkfast":

Bob will either rún — or walkfast.

Those rhythms and tonal patterns would be in line with your second interpretation:

Bob will either run (at some unspecified speed) or he will walk fast.

Your first interpretation

Bob will either run fast or he will walk fast.

would be quite unusual, running counter to expectation, yet not impossible; it would require something like this:

Bob will either run or walk ... fast.

That is, a marked disambiguating pause after walk, to yoke "run or walk", so that the adverb fast would be a kind of afterthought: "but no matter whether he runs or walks, it won't be slowly, I can tell you that!"

  • Very well put! What would you say about this sentence if it were read in text? Is it an "incorrect" sentence because it is entirely ambiguous?
    – nt22
    Jan 20, 2015 at 19:54
  • I would write Bob will either run, or walk fast. Punctuation can reflect natural pauses. Most people would understand that written sentence to mean your #2.
    – TimR
    Jan 20, 2015 at 19:55

It's not resolved in your first example, which really is ambiguous. Are you asking for some best way to resolve it by rephrasing? Anything that works.

  • Yeah my question is whether a statement that has that kind of format is always going to remain ambiguous. I'll update my post to clarify.
    – nt22
    Jan 20, 2015 at 19:40
  • 1
    Yes, a statement with a conjunction of two verb phrases followed by a verb phrase modifier, such as "fast", will always be grammatically ambiguous, because the conjunction of the two verb phrases is itself a verb phrase. So either the conjunction could be what is modified or the second conjunct. (Some may prefer the terms "disjunction" and "disjunct".) But semantic or other non-grammatical factors could rule out one potential interpretation.
    – Greg Lee
    Jan 20, 2015 at 20:53

"Or" in your sentence:

"Bob will run or walk fast."    

is ambiguous. That is simply a quirk of English. If the context is not obvious, you must include more specificity to be more clear.

  • So if you're using "or" to separate adverbs, are you "not allowed" to use adverbs in that sentence (without restructuring the sentence)?
    – nt22
    Jan 20, 2015 at 19:48

T Romano comes close to one solution for disambiguating in written English:

Bob will either run – or walk – fast.


Bob will either run – or walk fast.

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