Review—In our last class session, we were introduced to a new form of argument called a diagnostic
argument. A diagnostic argument differs from our previous form of argument in that in a diagnostic
argument the conclusion explains some of the support. The support that the conclusion(s) explains
are called trace-data. Trace-data(TD) become the object of explanation. Non-trace-data (NTD)
is all other support in the argument that aids in understanding but is not the object of understanding.
Thus in a diagnostic argument you will have something like the following:

S1: TD
S2: NTD
S3: NTD
S4: TD
-----------
C

C explains S1 and S4. S2 and S3 are used to support the conclusion, but the conclusion does not
    explain S2 and S3. (Remember the two directions)

For example,
S1: There is water all over the kitchen floor.
S2: The faucet is shut off and there is no water in the sink.
S3: The plumbing was new two years ago.
S4: Water is leaking out of the sink cabinet.
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IQ—Why is there water on the kitchen floor?
DR1—A pipe broke under the sink.
DR2—The sink has overflowed.
DR3—A bucket of water under the sink is leaking.

Notice, none of the DR’s explain S2 and S3, but they do explain S1 and S4.

Further Refinement of Trace-Data

We want to continue to refine our vocabulary, which will enable us to further articulate the relevance
of support in an argument to a conclusion—thus either increasing or decreasing the plausibility ranking
of the various DR’s. We will do so by breaking down our two main terms: trace-data and non-trace
data.

Trace-data is broken down into: central trace-data and peripheral trace-data. Central trace data are
often what define a case and will be what the all of the serious rivals are trying to explain. The relevance
of CTD consists in determining the list of serious rivals: these are what a rival (DR) must account for a
rival be relatively plausible and to make it on the serious rival list.

In our example just given, S1 and S4 would clearly be CTD. Serious rivals have to explain why there is
water on the floor and why there is water coming out of the sink cabinet. In our Birmingham blast case,
S1 would be central trace-data.

Peripheral trace-data may be relevant, positively or negatively to a single rival. In our Birmingham blast
case, S2 and S3 would be peripheral trace data because only the IRA is explaining those—it affects it
positively.

The relevance of PTD rests in their being easy or hard for a particular rival (DR) to explain. An item of
peripheral trace-data this is hard for a rival to explain is called an ‘explanatory hurdle’ for that rival.
In our Birmingham blast case, an explanatory hurdle for the Taliban and the KKK as DR’s is S2—
The bomb threat calls, and S3—There were previous blasts linked to another group. The point of the
notion of an explanatory hurdle is that the most plausible DR will either have none or have the fewest
hurdles to clear.

Summary: There are two types of trace-data. Central are what the all the DR’s are trying to explain.
Peripheral are what are relevant to a single DR. When a rival has a hard time explaining some support
that support is called an explanatory hurdle. Explanatory hurdles may be a sign that you do not have the
most plausible rival.

Analytic Summary: Trace-data may have four different kinds of impact on an argument and thus four
different articulations of relevance.

1. TD may determine the serious rival list (central TD)
Relevance: All rivals must explain it.

2. TD may add one rival to the list.
Relevance: Cn (some particular rival) easily explains it
 and that puts Cn on the list.

3. TD may move a rival up (change ranking or gaps)
Relevance: Cn easily explains it and thus ranks higher.

4. TD may move a rival down or off the list (hurdle).
Relevance: Cn has difficulty explaining it and thus ranks lower.

Further Refinement of Non-Trace-Data

Non-trace-data is broken down into two kinds as well: type-a and type-b.

Remember the function of non-trace-data is to supply explanatory resources to the argument. And,
what exactly counts as ‘supply’ here is tricky. The point here is very subtle, too subtle for our purposes.
The main thing is that your recognize non-trace-data as being distinct from trace-data.

Summary: The two-types of non-trace-data: type-a shows what is available as trace-data for an argument,
where as type-b shows what is available to help the various rivals explain an argument’s trace-data. The
difference is that type-a indicates trace-data for an argument, where as type-b indicates what’s available
to help explain the trace-data.