linguistics1-6  Exercise 2: Entailment, Idioms and Ambiguity
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Entailment:

  (a) Anna killed the spider  ->  The spider died.        YES, entails.
      "Kill" means "cause to die", so if the first is true, the second must be.

  (b) Anna hit the spider     ->  The spider died.        NO, does not entail.
      She may have hit it and the spider survived. The second sentence may
      be true, but the first does not guarantee it.

  (c) He kicked the bucket    ->  He died.                YES, entails, but
      only on the idiomatic reading.

Why (c) is a problem for compositionality:

  Compositionality says the meaning of a sentence is built from its words
  and structure. Nothing in "kick" + "the" + "bucket" gives the meaning
  "die". The meaning belongs to the whole phrase and is stored in the
  speaker's memory as a unit. Idioms therefore have to be learned as
  complete items, which is why they are hard for second-language learners
  (and also why they cannot be translated word for word).

Two readings of "I went to the bank":

  1. I went to the financial institution (where money is kept).
  2. I went to the side of a river.

  This is LEXICAL ambiguity: one word, two meanings. It is different from
  the structural ambiguity of "I saw the man with the telescope" (Chapter 5),
  where the words are fixed but they can be grouped in two ways.