I've always had a hard time immediately understanding the differences between passive, causative, and causative-passive. If I really sit down and try to work out the meaning I can generally get it, but I have a bad habit of just skimming over it.
One verb that is giving me trouble is 笑う:
The passive is 笑われる, or "to be laughed at". This seems pretty straight-forward.
たけしさんはメアリーさんによく笑われます。 Takeshi is often laughed at by Mary.
The causative is 笑わせる, or "to make laugh, to let laugh". Again, this makes sense to me.
彼かれは子供こども達たちを笑わせた。 He made the children laugh.
What I don't understand is the the causative-passive, 笑わせられる. My understanding of it is that it follows the pattern of "is made to do", that someone is made to do something that they don't want to do. But how does this work with laughter? It seems to me that this is the same meaning as "being made to laugh". The only other thing I can think of is "was made to laugh at someone", like in a peer-pressure sort of situation.
Take this JLPT practice question:
△△さんの冗談には、いつも思わず 笑わせられた 。
The wrong answers include 笑われた, and 笑わせた.
Why is the answer the causative-passive (せられた), and not the causative (せた)? What is the difference in meaning? Is the causative out-right wrong here, or is it just less-right or natural then the causative-passive? Is there a clue in the sentence structure that I'm missing?