  We address the task of explaining the effects of perturbations in procedural
text, an important test of process comprehension. Consider a passage describing
a rabbit's life-cycle: humans can easily explain the effect on the rabbit
population if a female rabbit becomes ill -- i.e., the female rabbit would not
become pregnant, and as a result not have babies leading to a decrease in
rabbit population. We present QUARTET, a system that constructs such
explanations from paragraphs, by modeling the explanation task as a multitask
learning problem. QUARTET provides better explanations (based on the sentences
in the procedural text) compared to several strong baselines on a recent
process comprehension benchmark. We also present a surprising secondary effect:
our model also achieves a new SOTA with a 7% absolute F1 improvement on a
downstream QA task. This illustrates that good explanations do not have to come
at the expense of end task performance.
