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Do these two sentences mean the same?

  1. Nothing is an offence which is done by a person who, at the time of doing it, is, by reason of intoxication, incapable of knowing the nature of the act, or that he is doing what is either wrong, or contrary to law: provided that the thing which intoxicated him was administered to him without his knowledge or against his will.

  2. Nothing is an offence which is done by a person who, at the time of doing it, is, by reason of intoxication, incapable of knowing the nature of the act, or that he is doing what is either wrong, or contrary to law: unless that the thing which intoxicated him was administered to him without his knowledge or against his will.

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    I would say that the two words mean the exact opposite; provided that means only if it is the case and unless means only if it isn't the case. Commented Sep 6, 2023 at 14:38
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    @KateBunting There's no only type meaning encoded on those examples - although it is implied. So in: "I reply to emails within 24 hours, provided I'm not ill" it doesn't mean that I definitely won't answer if I am ill. Similarly with "I reply to emails within 24 hours unless I'm ill". Commented Sep 6, 2023 at 16:36
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    @Araucaria-Him - I'm not sure about that; but the point I was making was the contrast between "provided I'm not" and "unless I am". Commented Sep 6, 2023 at 17:37
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    ... which a dictionary will point out. Commented Sep 7, 2023 at 14:22
  • @ryang - So Collins Dictionary is wrong in your eyes? Commented Sep 8, 2023 at 12:14

5 Answers 5

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The multiple negations of various sorts make it a little difficult to track what is going on in the Original Poster's examples. That's quite normal; it's what multiple negations do.

The second sentence of the Original Poster's does not mean the same as the first. Indeed, it would be a very strange state of affairs if the second sentence were true. The meaning is along the following lines:

  • Generally, if a person is too drunk to know what they are doing or to know that it's illegal, they aren't committing a crime. However, if someone spikes their drink without them knowing and they do the same thing, they are committing a crime.

So in such a case, if I gleefully drank a bottle of whisky and then stole a police car and drove it home, I would not be committing a crime. But in contrast, if someone put a load of vodka in my pint of lemonade and I didn't know about it, and I stole a policeman's car and drove it home, I would have committed a crime.

The first example, however, says what we might expect, that:

  • People are not committing a crime when they're too drunk to know what they're doing - if someone spikes their drink.

This first example implies, but does not state, that people are committing a crime if they knowingly drink so much that they don't know that what they're doing is illegal.

Q, provided P is logically equivalent to Q, if P. In contrast, Q, unless P is equivalent to Q, if not P.

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  • Yes. @Araucaria And would you explicitly state that #1 makes more sense than #2? Commented Sep 6, 2023 at 14:28
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    @YosefBaskin Yes, god idea. Have done. Commented Sep 6, 2023 at 14:56
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    The second sentence sounded wrong but I wanted to make sure as this is something drafted by legal luminaries.
    – Ramkay
    Commented Sep 6, 2023 at 17:03
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In any pair of sentences of the form

A provided B

and

A unless B

the two have essentially opposite polarities.

Compare Walking in the street will be safe provided the ice melts and Walking across the pond will be safe unless the ice melts. The former asserts that the ice’s melting is a sufficient condition for safety, whereas the latter asserts that it’s a sufficient condition for danger.

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The clausal complement of provided expresses a necessary condition.

The clausal complement of unless expresses an exceptional condition.

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Let... denote...
X(s,p) The administration of substance s to person p had been without their knowledge or against their will.
Y(p,a,s) While person p was committing act a, they were, due to intoxication by substance s, incapable of knowing the nature of the act or that the act is wrong or contrary to law.
Z(a) Act a is not an offence.
  1. Nothing is an offence which is done by a person who, at the time of doing it, is, by reason of intoxication, incapable of knowing the nature of the act, or that he is doing what is either wrong, or contrary to law: unless that the thing which intoxicated him was administered to him without his knowledge or against his will.

The word ‘unless’ literally means ‘if not’.҂ Rephrasing the above verbiage:

  • an act is not an offence if committed by a person while, due to intoxication, incapable of knowing the nature of the act or that the act is wrong or contrary to law, if the substance that intoxicated them had been administered with their knowledge and not against their will
  • if   not X   then   ( if Y then Z )
  • equivalently:    if   ( not X and Y )   then   Z.

Shockingly, this law considers committing a wrongful act due to lack of judgement due to having willingly taken drugs to not be an offence.

  1. Nothing is an offence which is done by a person who, at the time of doing it, is, by reason of intoxication, incapable of knowing the nature of the act, or that he is doing what is either wrong, or contrary to law: provided that the thing which intoxicated him was administered to him without his knowledge or against his will.

The phrase ‘provided that’ means ‘if and only if’ (justification, citing Collins and Oxford). Rephrasing the above verbiage:

  • an act is not an offence if committed by a person while, due to intoxication, incapable of knowing the nature of the act or that the act is wrong or contrary to law, if and only if the substance that intoxicated them had been administered without their knowledge or against their will
  • X   if and only if   ( if Y then Z )
  • equivalently:     not X   if and only if   ( Y and not Z ).

This law is stronger than necessary, stipulating extraneously that committing an act while intoxicated after having willingly taken drugs necessitates incapability of knowing that the act is wrong.


This is the clearest and most sensible alternative phrasing:

  • an act is not an offence if committed by a person while, due to intoxication by a substance that had been administered without their knowledge or against their will, incapable of knowing the nature of the act or that the act is wrong or contrary to law
  • if an act was committed by a person while, due to intoxication by a substance that had been administered without their knowledge or against their will, incapable of knowing the nature of the act or that the act is wrong or contrary to law, then the act is not an offence
  • if   ( X and Y )  then   Z.

҂Supplementary note

The word ‘unless’ literally means ‘if not’. For example, the observation “in the 1940s, unless she wore gloves, a woman wasn't considered properly dressed” does not additionally claim that every glove-wearing woman in the 1940s was considered properly dressed, and the directive “don't compliment unless you mean it” carries no instruction to give a compliment whenever one means it.

As such, ‘W unless Z’ can be paraphrased as ‘W and Z are not both false’, which is equivalent to ‘at least one of W and Z is true’, which is equivalent to ‘W or Z’, where the connective ‘or’ is in the inclusive sense; in other words, the relation ‘unless’ is, strictly speaking, a disjunction. (In practice though, the relation ‘unless’ is frequently intended to convey the exclusive disjunction—in other words, for ‘W unless Z’ to mean ‘W or Z but not both’.)


Reply to comment

@ryang - So Collins Dictionary is wrong in your eyes?

@KateBunting  Your linked Collins definition is correct to say

  • use ‘unless’ to introduce the only circumstance in which a statement you are making is not true;

this says that the statement

  • B unless A

can be rephrased as

  • the only circumstance in which B is not true is A being true
  • if B is not true, then A must be true
  • A if not B,

which is logically equivalent to

  • B if not A.

QED. (Unfortunately, however, immediately following this main definition, Collins unwittingly supplies a contradictory Usage Note, saying

  • ‘unless’ is used to introduce the only situation in which something will be true

instead there! The phrase is not true in the dictionary's own, foregoing definition has been erroneously transposed here as will be true.)

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    The word but is logically equivalent to and, but it doesn't literally mean and. The same is true for unless and if not. Try the following, for example: "This chair will break unless you don't sit on it". And in the same way provided does not mean if, although they are logically equivalent: "Provided you win the lottery tomorrow, you won't have any problems paying your mortgage". Commented Sep 8, 2023 at 10:59
  • @Araucaria For sure, I agree with your first sentence: 'but' does not literally mean 'and' because only the former indicates a contrasting. As for the rest of your comment, we are actually coming from the same place: in everyday usage, 'provided that' and 'unless' frequently carry connotations beyond their literal meanings, and implicature is precisely what is not literally expressed. My comment under the main OP expands on this. Since this entire discussion is critiquing legal writing, we want to read the given text literally and conservatively without projecting stronger meanings.
    – ryang
    Commented Sep 8, 2023 at 11:41
  • I think Collins means "the only situation in which a woman was properly dressed was if she was wearing gloves" and "you should only make compliments if you mean them". Commented Sep 8, 2023 at 13:31
  • @KateBunting Yes ("the only situation in which a woman was properly dressed was if she was wearing gloves"; "you should make compliments only if you mean them")—precisely as I've explained in my appended reply above. Observe that here and in Collins's definition of 'B unless A' (which contains no denotation that A being true necessitates B being untrue), the word "only" is referring to the TRUE/false parity of A. Thus, the preceding instance of "only if" is consistent with its technical meaning, 'entails',
    – ryang
    Commented Jun 19 at 6:58
  • which is in fact a weaker denotation than the 'if and only if' meaning that you intended in your comment-reply to Araucaria (I would say that 'provided that' means '(if and) only if it is the case', whereas 'unless' means '(if and) only if it is not the case'). Incidentally (and summarising my Answer): I agree with Araucaria that ‘unless’ means ‘if not’, whereas I agree with you that ‘provided that’ means ‘if and only if’.
    – ryang
    Commented Jun 22 at 9:15
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Breaking down these sentences, the first portion prior to the conjunctions provided & unless describe an intoxicated individual and basically state that they aren't accountable for their actions. However, the conjunctions and following text determine when this rule can be applied.

After the conjunctions, both of these sentences describe the situation of an individual being involuntarily intoxicated:

  • In the first case, this person would be held accountable for unlawful acts while intoxicated unless they were involuntarily intoxicated. (The conjunction here provides an exception to the rule)

  • In the second case, they would not be held accountable for unlawful acts while intoxicated unless they were involuntarily intoxicated. (The conjunction here stipulates a condition which must be met for the rule to be applied)

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