PT103 · S3 · Q19 Over the past 20 years, skiing

Just because the argument only mentions broken legs, ankle injuries, and knee injuries doesn't mean that it's thinking that those are the only injuries there are. We're never allowed to think "the only X's mentioned = the only X's there are".

The only causality in the paragraph is background fact that ski injuries have lessened due to better equipment. But the author's conclusion and evidence have no causality in them. It's just numbers and percents. The conclusion is that there are more knee injuries than before. The evidence is that knee injuries went from 11% to 16% of all ski injuries. That isn't inferring the effect of any cause. That's just stating a quantitative idea. Also, there's nothing inherently wrong with inferring differing effects from the same single cause. It's possible that a single cause (like more CO2 in the atmosphere) could cause damage to some ecosystems while also making plants photosynthesize more efficiently elsewhere.

Since this answer starts with fails to consider / ignores the possibility, we can ask ourselves if the idea that follows would Weaken. Could we object to this argument by saying, "Hey, author -- the total number of skiers has increased!" No, that would just lend support to her conclusion. She thinks there are more knee injuries than before, so if there are more skiers than before that would help her case.

This answer accuses the author of making an argument she never made. It's saying the author was arguing something like this: "Our store sells only products X, Y, and Z. Last month we sold 30% more X than usual, 40% more Y, and 50% more Z. Thus, last month we sold 25% more than we usually do." The overall uptick in sales would have to be somewhere between 30%-50%, since all the constituent parts moved by that degree. This answer accuses our author of thinking that even though the overall decrease in injuries was 50%, the decrease in each category was greater than 50%. The author does think in the category of leg/ankle injuries, the decrease was greater than 50% (it was 90%). But the author isn't thinking that all other categories decreased by more than 50%; in fact knee injuries is a category that our author thinks has increased.