A straw man twists the other side's view. A red herring leaves it behind altogether.
Key idea
A red herring changes the subject to a different issue, then treats the original question as if it had been settled.
Why it works
The new topic may be true and even interesting, but it is not about the question. Talking about how splintery the old playground was does not show that the new slide is cool enough to use. The first question is still open.
Worked example: A dropped question
Parent: "Did you feed the dog this morning?" Child: "Did you know dogs are some of the smartest pets? So the dog is fine."
- The question: was the dog fed?
- The reply: facts about dogs in general.
- The reply is treated as if it settled the question.
Answer: Red herring.
Worked example: Same topic, not a red herring
Ava: "The bake sale lost money because we bought too many supplies." Ben: "We also sold fewer cookies because it rained, so supplies were only part of it."
- Ben's point is about the same question: why the sale lost money.
- He adds a cause; he does not change the subject.
Answer: Not a fallacy.
Common mistake
Calling any change of topic a red herring. Raising a new topic openly is fine. It is a fallacy when the new topic is used as though it answered the first. Ask: after the reply, has the original question been answered?