I am yet to learn about ambiguity and sound arguments but am attepting to make the following argument sound.

  1. All criminal actions are illegal

  2. All murder trials are criminal actions


  1. All murder trials are illegal

The argument is unsound because Premise (2) is not true. There is ambiguity around the phrase "Criminal Action" which is not consistent among both premises.

Is the ambiguity Lexical or structural ambiguity. My thinking is Lexical even though two words are involved.

The following is my attempt of making the argument sound but I am concerned that now the argument is contexually different.

  1. All criminal actions are illegal

  2. All murders are criminal actions


  1. All murders are illegal
  • Hi @HunanRostomyan. This question is an extention of a question you helped me with yesterday. Any help on this would be appreciated.
    – Trish
    Apr 29, 2015 at 3:40
  • 1
    Now the argument is sound ... Apr 29, 2015 at 18:38
  • A philosophical consideration is whether any of the two premises are true in e.g. the US or Russia. Or Norway. I would say no. May 11, 2015 at 10:31
  • Lawyers may differentiate "criminal" vs "civil" "actions", where "action" is in the sense of "a set of legal activities taken together either all of which or none of which should be completed". That contextual meaning of "action" is quite different from the sense in which the crime itself was an "action". (In a US court, usually, a suit is an action, and a murder is an act.) Is that the misunderstanding involved?
    – user9166
    Jun 10, 2015 at 20:22

2 Answers 2


It's lexical. In 1) you've used Criminal as an adjective to mean that the action is criminal. In 2) you've used it to mean actions pertaining to criminal things.

The second use isn't common in English which is presumably why you stated that it isn't true.


so to make your original formulation consistent:

  1. All criminal actions are illegal

  2. All murder trials pertain to criminal actions


  3. All murder trials pertain to illegal actions


The argument is valid, but does leave room for some ambiguity.

The first is true just by virtue of the fact that 'illegal' and 'criminal' are interchangeable in the jurisprudential argot.

The second is doubtful given that some murders (if we define 'murder' as 'killing a person') are done from the self-defence and hence wouldn't be considered criminal. Otherwise, the premise is analytic, to wit, true by virtue of the terms it employs. For any act to be classified as 'murder', it is necessary that the act is classified as criminal.

If we reformulate your argument given the above distinctions, then we have:

  1. All criminal actions are criminal.
  2. All murders are criminal actions.

C: All murders are criminal

Thus, now the argument is sound and unequivocal.

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