Ruling Out Alternate Explanations (Defender)

Read the following argument and evaluate the subsequent statement.

Historian: During the 1880s, the National Telegraph Company's adoption of the duplex telegraph system—which permitted simultaneous bidirectional transmission—coincided with a 30 percent reduction in garbled dispatches. Clearly, the continuous electrical current required by the duplex system actively suppressed the ambient magnetic interference that typically causes signal degradation.

Statement: A necessary assumption of the historian's argument is that the installation of the duplex telegraph system did not simultaneously require replacing the company's existing unshielded wires with heavily insulated cables.

In Logical Reasoning, a 'Defender Assumption' is a necessary assumption that protects a causal conclusion by ruling out a specific alternative explanation or vulnerability. Match each causal argument and its corresponding objection (Left) to the precise defender assumption (Right) that the argument MUST make to survive the objection.

During the late nineteenth century, the rapid integration of mechanized looms in the textile mills of the Solway region was immediately followed by a sharp decline in the number of itinerant weavers seeking contract work there. Economic historians have concluded that the operational efficiency of the mechanized looms eliminated the demand for manual weaving, directly causing the itinerant workforce to abandon the region.

Evaluate the logical requirements of the historians' conclusion.

Statement: The argument fundamentally relies on the assumption that a severe shortage of raw materials did not force the Solway textile mills to drastically reduce their overall operations during that same period.

Is the statement above true or false?

Maritime Analyst: Three years ago, several major shipping companies voluntarily installed novel hull-lubrication systems on a portion of their cargo fleets. A recent analysis shows that over the past two years, the vessels equipped with these systems consumed, on average, 12 percent less fuel per voyage than comparable vessels in the same fleets that were not equipped with the systems. This clearly demonstrates that the hull-lubrication systems are highly effective at reducing fuel consumption.

Which one of the following is an assumption required by the maritime analyst's argument?

A recent municipal review of urban residential areas revealed that neighborhoods with a higher density of community gardens have significantly lower rates of property crime. City planners concluded that the presence of community gardens must foster social cohesion and neighborhood watchfulness, which in turn actively deters criminal activity.

Determine whether the following statement regarding the argument is true or false: A necessary assumption of the city planners' reasoning is that neighborhoods with preexisting lower rates of property crime do not systematically attract more civic funding and volunteer resources for community garden projects than neighborhoods with higher crime rates.

An urban planner argues: 'Last year, our city installed a new smart traffic light network at ten major intersections. Over the past twelve months, traffic accidents at these specific intersections decreased by 30%. Therefore, the new smart traffic lights directly caused this significant reduction in accidents.'

Match each potential alternate explanation (objection) on the left with the specific defender assumption on the right that the urban planner must rely on to neutralize that threat to the causal claim.