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4.1 Reasons for Reasons

One reason can provide evidence in support of another.  This is the simplest case of a multi-layer argument.

Consider this reasoning from Apollo Moon Landings:

The shadows of the astronauts and their equipment in the Apollo pictures seem to point in different directions.  This suggests that artificial lighting was used and therefore the pictures were taken in a studio on earth. [Based on 5.1]

This passage contains two simple arguments:

Here are the two simple arguments mapped separately.  Notice that the first argument provides support for the second.  The contention of the first argument is in fact a premise in the second.

Here are the two arguments mapped as a single multi-layer argument.

A multi-layer argument is an argument in which there are reasons or objections bearing upon reasons or objections.