The Council Memo on Parking Minimums
A city council memo argues as follows. (1) If the city removes downtown parking minimums, developers will build fewer parking spaces. (2) In the cities we reviewed where rents fell, developers had built fewer parking spaces. (3) Therefore removing the minimums will lower rents here. The memo adds: "Every study in our file that found a rent effect was funded by an advocacy group, so none of those studies is reliable." A councillor responds: "You can't dismiss them like that - those groups have been right about other things." Later in the meeting another councillor says: "Either we keep the minimums or rents rise; rents are going to rise; so we keep the minimums." The council must vote in two weeks, and the planning department wants to know which of the three moves are sound, which are merely valid, and which are neither.
1. Formalize premises (1)–(3) and determine whether the argument is valid. Give a countermodel.
Read the worked answer
Let R = the city removes minimums, F = developers build fewer spaces, L = rents fall. The memo's premises are R → F and L → F ("cities where rents fell were cities where fewer spaces were built" is a claim about the L-cases, not about the R-cases), with conclusion R → L.
The form is: R → F; L → F; therefore R → L. This is invalid - it affirms the consequent in a relational form, and in categorical dress it is the fallacy of the undistributed middle (All R are F; all L are F; therefore all R are L). F is never distributed.
A countermodel suffices: suppose R is true (the city removes minimums), F is true (developers build fewer spaces), and L is false (rents rise because a regional employment boom raises demand faster than supply). Both premises are true and the conclusion false, so the form is invalid.
The diagnosis matters for policy: the argument fails at the level of form, so no amount of additional数据 about the reviewed cities can repair it. What is needed is either a premise linking R directly to L, or a causal model explaining why supply reduction lowers rents rather than raising them. The memo confuses a correlate of the conclusion with a route to it.
2. Evaluate the funding objection and the councillor's reply. What is the correct epistemic response to source-directed criticism?
Read the worked answer
The memo commits the genetic fallacy if it moves from "funded by an advocacy group" to "unreliable." Provenance is not truth-value. But the councillor's reply - "they've been right about other things" - is worse: it is an irrelevant appeal that does not address reliability in this domain at all.
The defensible middle position treats funding as evidence about the probability of bias, not as a verdict. Industry or advocacy funding correlates with results favourable to the funder, so it raises the prior of directional error and justifies scrutiny: Was the outcome pre-registered? Was the model pre-specified? Do independent replications with different funding reach the same result? Does the effect survive adjustment for demand shocks, zoning changes and construction costs?
Applied here, the correct move is a sensitivity analysis: separate studies by design quality, not by funder alone, and see whether the rent effect appears in the well-identified subset. If it appears only in the advocacy-funded, weakly identified studies, the council should discount it - not because of the funder, but because of the confounds. If it survives, the funder is irrelevant. The memo's blanket dismissal and the councillor's blanket defence are both evasions of the methodological question.
3. Analyze the councillor's disjunctive argument. Distinguish validity from soundness, and identify any implicit premise doing the work.
Read the worked answer
Let K = we keep the minimums, and U = rents will rise. The argument is K ∨ U; U; therefore K. This is the fallacy of affirming a disjunct: the disjunction is inclusive, so U's truth is compatible with K's truth, but it does not require it. Countermodel: K is true and U is true (we keep the minimums and rents rise anyway). So the form is invalid as stated.
The argument becomes valid only if the disjunction is read as exclusive ("either we keep the minimums or rents will rise, but not both"). That reading is doing all the work and is not defended. It is also a false dilemma: rents might fall without removing the minimums, for example through inclusionary zoning or a supply subsidy.
Separately, soundness is a further question. Even a valid version requires the premise "rents will rise" to be established, and that is precisely the proposition the memo's argument (1)–(3) was supposed to support and failed to. So the council is being offered an argument that is invalid on its natural reading, valid only on an undefended exclusive reading, and unsound on either reading unless the rent forecast is independently supported. Recommend that the planning department reject the inference and commission the forecast.