conflicting pronouncements it hardly follows 
that p A, P is in fact true. The same con-
sequence follows by elementary laws of prob-
ability from taking "X (a generally veracious 
but imperfect source) maintains p, therefore 
p is highly probable" as a correct inference. 3 
Thus Rescher has shown that for an essen-
tially subject-based (for two sources X and 
Y, or greater than two) appeal to authority, 
the type of inference can be neither deduc-
tive nor inductive. In essence, these dis-
proofs reflect the conception that for mul-
tiple authorities that are imperfect and may 
be expected to have conflicting pronounce-
ments, deductive and inductive models of 
inference are "too perfect". Hamblin's and 
Salmon's conceptions of the ad verecundiam 
are too idealized to adequatiry represent the 
practice of appeals to imperfect authorities 
whose pronouncements may clash. But con-
fronted by contradiction we mus~ not give up 
--even though deductive or inductive logics 
give no further guidance--but press on to 
resolve the contradiction by means of plausi-
bility theory. 

Now that we have eliminated the deductive 
and inductive models, and identified plau~i­
ble inference as a preferable model for the 
type of argument exemplified by the ad 
verecundiam, it would seem the way is open 
to an analysis of this fallacy. And so in-
deed it may be, but this is not a project we 
shall attempt here. Suffice it to say for 
the moment that as Rescher conceives it 
plausible inference is not subject-matter-
sensitive, so at very least plausibility 
theory will have to be conjOined to a theory 
of the subject-matter content of propositions 4 
in order to be adequate to the full ad 
verecundiam. These refinements aside how-
ever, we are at least in the position now of 
being able to identify one noteworthily in-
sidious form of the ad verecundiam. 

The fallacy we allude to occurs where an 
appeal to authority is construed so strongly, 
or such a lack of specification of its type 
of argument has transpired, that the argument 
is taken to have (a) deductive, or (b) in-
ductive correctness. Yet if the appeal is 
ment to be taken--as it should be generally--
to a less than perfectly veracious authority, 
then its construal as (a> or (b) is falla-
cious. The specific fallacy here lies not in 
the appeal to authority as such, but in the 
spurious escalation of the appeal towards a 
claim to a source of truth that is more 
perfect or infallible than a plausible argu-
ment has any logical right to be. In short, 
this fallacy is to misidentify the type of 
argument. 

This particular error is of course not the 
only way in which an ap~eal to authority can 
go wrong, and elsewhere we have suggested 
that ad verecundiam is an umbrella concept 
for several specific pitfalls of argument 
from authorities. But this particular spe-
cies of the ad verecundiam is an important 
one, we think, in teaching students how to 
confront and deal with the fallacies, be-
cause it underscores the need to take into 
consideration identification of the type of 

6 

argument as a necessary skill of informal 
logic. The first step in attempting to 
adjudicate any allegation that a fallacy has 
been committed is to ask the question "What 
(exactly) is the argument?" Answering this 
question involves more than simply specifying 
a set of propositions--as in the approach of 
formal logic--it includes, among other tasks, 
specification of the type of argument that 
has been advanced. 

Notes 

lsee our article "Fallaciousness Without 
Invalidity?" Philosophy and Rhetoric, 9, 
1976, 52-54, ana "Formal~gic ana the Logic 
of Argument" to be presented at the 6th 
International Congress of Logic, Methodoloqy 
and Philosophy of Science in Hannover, 
Germany, August, 1979. 

2see our article "Argumentum Ad 
Verecundiam," "Philosophy and Rhetoric 7, 
1974, 135-153. - , 

3The proof, parallel to the one above, is 
given by Rescher (1976, p. 3). 

4For such a theory, the reader should look ., 
to Douglas N. Walton 'Philosophical Basis of 
Relatedness Logic,' Philosophical Studies, to f 
appear. 

References 

C. L. Hamblin, Fallacies, London, Methuen, 
1970. 

Nicholas Rescher, Plausible Reasoning, 
As sen/Amsterdam, Van Gorcum, 1976. 

Wesley Salmon, Logig, Englewood Cliffs N.J., Prentice-Hal~, ~ 63. ' 

discussi on notes 

A NOTE 'IN THE "SURPRISE TEST" PUZZLE 

Harry A. Nielsen (University of Windsor> 

pre 
he 
Fri 
bet 
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that is 
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dity su' 
bright 
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--Sorry 
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That is 
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The 
test ele 
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class ~ 
does nc 
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student 
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could 11 
school. 
doesn't 
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prise j 
lapse c 
show a 

A schoolteacher announces to her 
class that there will be a surprise 
test during the followinq week. She 
specifies that by a "surprise test" 
she means one which no one could 
reasonably predict while walking to 
school. Immediately, one of her 
~righter students claims that she has 
contradicted herself. He offers this 
argument: The surprise test could 
take place on Friday, for if there had 
been no test up until Friday, then 
from that fact and the knowledge that 
there will be a test any student could 

~ point, 
[ a posit 

until 1 
Witt 

if whai 
tent!al 
take he 



has 
lat 
lis 
rying 
1 of 
asks, 
It 

jut 

)qic 

.oqy 

is 

look 
i of 
~, to 

,uen, 

predict while walking to school that 
he was going to be given the test on 
Friday. So the test must take place 
between Monday and Thursday. But the 
same argument works for Thursday. 
That is, on Thursday morning, any 
student could deduce from the facts 
that there can be no surprise test on 
Friday, and that there will be a test, 
and as it is Thursday the correct pre-
diction is that the test will be given 
that day. Clearly the argument can be 
extended to show that the test cannot 
be given on Wednesday, Tuesday or Monday. 
The conclusion is that the test cannot 
be given at all. 

The teacher heard this objection 
out, and then gave the test on the 
following Tuesday, surprising, in 
the required sense, everyone. 

The puzzle here is to see what 
has gone wrong witH the argument. 
Clearly the teacher can give the 
surprise test. How rs-it the case, 
then, that an apparently impeccable 
argument can produce the conclusion 
that no surprise test is possible? 

******************** 
It is odd to confront a piece of reasoning 

that is valid only on some particular Thursday 
evening or Friday morning, but this very od-
dity suggests a key to the puzzle: time. The 
bright student in the story says, "If Thursday 
~nt by, and still no test, it couldn't be a 
surprise on Friday, so we can scratch Friday." 
--Sorry, but Friday has this about it, that 
~u can't scratch it for real until Thursday. 
That is, you can't scratch it for real by 
imaginin~ that Thursday's class has ended and 
ilius rullong Friday out. The reasoning in the 
puzzle derives its appearance of force from 
our forgetting that, for us humans, the whole 
time between the start of Monday's class and 
the end of Thursday's has to be lived through 
before' a student is in a position to downgrade 
the teacher's logic. It is within that se-
quence of days that the teacher can bring off 
her surprise test. 

The time-range in which she can spring the 
test extends from the start of Monday's class 
to near the end of Thursday·s. As Thursday's 
class passes its halfway mark, the student 
does not know if she will give the test in the 
minutes remaining. Suppose she does; then the 
student will have no grievance, for the teach-

L er came through with the test at a time he 
could not predict for certain on his way to 
school. But what can the student say if she 
doesn't give the test on Thursday? "You let 
too much time go by-- now the element of sur-
prise is gone." This is hardly a lo~ical 
lapse on the teacher's part, though lot may 
show a bit of absent~indedness. The main 
point, however, is that her student is not in 
a position to make even that guarded judgment 
ootil the sands of Thursday's class run out. 

With these considerations in mind, I wonder 
if what we have here could be called an exis-
tential paradox, in as much as the puzzle can 
take hold of the student only if he forgets a 

7 

certain temporal feature of his,.human exis .... 
tence, namely that he cannot' reason himself 
forward to the end of the week, and then work 
backwards through time, &ut has to exist 
through the intervening days one by one and 
wait to see what each day brings. 

conference repo rt 5 

A PANEL ON INFORMAL LOGIC 

This Report was submitted &y Professor Samuel 
Fohr of the University of Pittsburgh at 
Bradford. 

A Panel on Informal Logic was presented 
a~ th7 Be~end Campus of Penn State Univer-
s1ty 1~ Er1e, Pa: at the Spring meeting of 
the Tr1-State Ph110sophical Association on 
April 21, 1979. The Panel was organized and 
ch~ired.by William Rapaport of the State 
Un1vers1ty of New York, College of Fredonia 
The other participants were Samuel Fohr o~ • 
the Uni~ersity of Pittsburgh at Bradford,4 
James L10tta of Lake Erie College, and Nelson 
Pole of Cleveland State University. 

~amuel Fohr pointed out that informal 
log1c courses could help people to arrive at 
more true beliefs and fewer false beliefs 
But the value of such courses could be se;i-
ously dimini~hed by how they were taught and 
the books wh17h were used. Philosophers have 
not been as r1gorous in their treatment of 
non-symbolic logic as they have been in their 
tre~tment of symbolic logic. Many writers of 
10g1c ~ks have been either sloppy or in-
correct 1n their definitions of basic terms 
such as "valid," "sound," "deductive argu-
In7nt," aJ?-d ~inductive argument." Any way of 
d~stinguloshl.ng between deductive and illduc-
tl.ve.arguments which is not based on the in-
tentloons of the person putting forward the 
argument is faulty. The word "fallacy" is 
use~ very 100s71y by many philosophers. 
~trl.ctly spea~1ng, a fallacy is an error in 
lonference.or l.n drawing a conclusion from 
so~ preml.ses. Yet philosophers have tended 
to lodentify assertions they take to be false 
as fa~lacies. ?n7 ref7rs to the fallacy of equat1ng determl.n1sm wloth fatalism, another 
to the fallacy of taking the rightness or 
wro~qness of actions to be related to the 
mot~ves for which they are done. Writers of 
~og1c.bO?ks ha~e gone far beyond this in 
1d7ntlofY1ng th1ngs as fallacies. Among other 
th1~gs the following have been identified in 
10g1c ~ooks as fallacies: questionable clai~ 
(pract1cally every claim is), emotionally 
charged language, suppressed evidenc~, dog-