I'm sure there have been occasions where you have observed a smile and you can sense it's not genuine. The most obvious way of identifying a genuine smile from an insincere one is that a fake smile primarily only affects the lower half of the face, predominantly with the mouth alone, and - the eyes don't really get involved. (from a book "Lie Catcher" by David Craig)(link1

  1. What's the exact meaning of 'with' in the bolded "with the mouth alone"?
    When referring to Merriam-Webster learner's dictionary(link2),
    1)definition 4 : using (something specified)
    or 2) definition 2 — used to say that two or more people or things are doing something together or are involved in something
    or 3) else??
    If the definition2 is right, I think it implies that 'a fake smile affects with the mouth alone' and this sentence is not correct because 'with the mouth alone' cannot be an object of the verb 'affect'. I'm so confused.

  2. If I change "you can sense it's not genuine" into "you could sense it was not genuine", is this right? Somebody says that it is possible.

Thanks in advance.

1 Answer 1


I'd understand this "with" to be "using". You are using your mouth to make a smile. You are not using the rest of your face.

Changing can to could is possible, but not needed. This this "be able to" meaning of can.

  • Thank you:) About question 2, When I change 'can' into 'could', the meaning is still in harmony with "you have observed a smile"?
    – Mcreaper
    Commented Jun 18, 2021 at 5:51
  • 1
    In my opinion could would be better. The author says 'you have observed a smile' (past tense) and then switches to present tense 'you can tell.' This is careless writing. Commented Jun 18, 2021 at 8:06

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