Logical Reasoning

PT10 · S1 · Q7 Slash-and-burn agriculture

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Slash-and-burn agriculture involves burning several acres of forest, leaving vegetable ash that provides ample fertilizer for three or four years of bountiful crops.

Conclusion

Forests in this region (the tropics) will eventually be permanently eradicated.

Evidence

Slash and burn makes ash that feeds big crops for 3 or 4 years, but after that, nutrients leach out of the soil and the land becomes too poor to farm.

New land is then cleared, starting the process again.

Most farming in the tropics uses slash and burn.

Evaluate

Necessary Assumptions can be identified by looking for a new idea in the conclusion. This conclusion predicts permanent eradication of forests but the evidence never made such a sweeping claim. The evidence did say that slash and burned land is only good for a few years, after which you gotta go slash and burn more land. But we could argue the Anti-Conclusion (the forests WON'T be permanently eradicated) if we posit, for example, that forests could regrow on slash and burned land after it's outlived its usefulness as farmland, or that there are protective regulations in place that limit how much land can be slashed and burned.

Goal

Look for an answer that connects the cycle of slash and burn explicitly to permanent eradication of forests (a Missing Link Assumption) or that rules out the possibility of some Anti-Conclusion objections (a Defender Assumption).

The argument depends on the assumption that

Correct
forests in the tropics do
Why this is right
The argument concludes that we'll end up with no more forest because of the slash and burn cylce in which we're slashing and burning ever more land for agriculture. But if burned land could regenerate back INTO forest, that argument falls apart. This argument assumes, then, that the land will NOT regenerate back into forest. Answer choice A is a Defender Assumption that neutralizes an objection. If you found this one hard to love because it introduced the idea of regeration, remember that it's OK for a Defender Assumption to bring in a new idea, so long as that new idea is part of a salient Objection to the argument that we need to neutralize in order for the argument to work.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
89% picked this
some other methods of agriculture
Unsupported Comparison
Condemning one method, plan or recommendation, that doesn't require assuming that some other method/plan/rec is actually better. That's a classic LSAT trap answer, and a flavor of Unsupported Comparison.
3% picked this
forests in the tropics are
Scope (nutrients, non-native plants)
Our conclusion about the impact of slash and burn doesn't hinge on any relationship between nutrient deficiency and non native plants.
3% picked this
slash-and-burn agriculture is particularly suitable
Premise Support
A premise tells us that "most farming in the tropics uses this method". We accept premises as true: they don't require assuming anything. Does D explain why most farming in the tropics uses slash and burn? Sure. But we don't need to assume that's true in order for the argument to work. Maybe most farming uses slash and burn because it's the cheapest, or the least labor intensive. Whatever the reason, the fact remains that most farms are doing it, and that's all we need for our argument.
4% picked this
slash-and-burn agriculture produces a more
Scope (1st year) / Unsupported Comparison
The argument already tells us that most tropical ag is slash and burn and, because of the neverending cylce, concludes we'll slash all the forest. We don't need to assume anything about the crops on the farmland, or how it stacks up against other types of ag in year one, or any other year.
1% picked this

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