Here's why:
* Metaphors are a broader concept: Metaphors use figurative language to compare two dissimilar things. They can be simple or complex, and they can be used in a variety of ways.
* Idioms are a specific type of metaphor: Idioms are figurative phrases that have a meaning that is different from the literal meaning of the words. They often use metaphorical language to convey a specific idea or feeling.
Think of it like this:
* Metaphor: "He's a lion in the boardroom" (Comparing someone's strength and confidence to a lion).
* Idiom: "He's got his head in the clouds" (Meaning he's not paying attention, not literally in the clouds).
Here's why idioms are considered a type of metaphor:
* Figurative Language: Idioms use figurative language to create a picture or image in the mind.
* Implied Comparison: They imply a comparison between the literal meaning of the words and the figurative meaning.
However, not all metaphors are idioms:
* Literal Comparisons: Some metaphors make direct comparisons, while idioms are more like fixed expressions.
* Flexibility: Metaphors can be more flexible and creative, while idioms have set meanings.
In short, idioms are a specific subset of metaphors. All idioms are metaphors, but not all metaphors are idioms.