Why does the argument about tubers and squashes commit an illicit-major fallacy?

The argument regarding tubers and squashes commits an illicit-major fallacy because it violates the fundamental logical rules for distribution.

In logic, a term is considered "distributed" when a statement refers to all members of that class. The fallacy of the illicit major occurs when the major term—the predicate of the conclusion—is distributed in the conclusion but was not distributed in its corresponding premise.

In the example provided:
* Premise 1: "All tubers are high-starch foods" (Here, "high-starch foods" is the major term and is undistributed because the statement does not refer to all high-starch foods).
* Premise 2: "No squashes are tubers."
* Conclusion: "Therefore, no squashes are high-starch foods" (Here, "high-starch foods" is distributed because the negative statement refers to the entire class of high-starch foods).

Because the major term "high-starch foods" is undistributed in the premise but becomes distributed in the conclusion, the argument is deductively invalid.1