2(3)7-11Responses.pdf


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ness logic is different from relevance logic 
--see \'ialton (19..79). 

References 

Otto Bird, "The Formalizing ·of the Topics in 
Mediaeval Logic," Notre Dame Journal of 
Formal Logic, 1

1 
1~J8;!'49 . -

Richard L . Epstein, "Relatedness and Implica-
tion , u Philosophical Studies, 36 , 1979 , 
137-173, 

R. H. Johnson and J , A. Blair , Logical Self~ 
Defense, Toron·to and New York , McGraw=-
Hill Ryerson, 1977 . 

Norman Kretzmann, trans. and ed ., William of 
Sherwood's Introduction to ~~g~c, 
Minneapolis, Onivers~ty OI ~nnesota 
Press, 1966. 

Douglas N. Walton, MPhilosophical Basis of 
Relatedness Log:i,c," Philosophical Studies, 
36, 1979 . 115-136 , 

Doug las N. Walton, "T,<7hy is the Ad Poi'ul urn a 
Fallacy?" Philosophy ~ Rhetor~c , to 
appear, 1980 . 

John Woods and Douglas t-lalton, "ArJumentum ad 
Verecundiam," Philosophy and etor~c, r, 
1974, 135-153. ---

John Noods and Douglas Walton, "Ad Hominem , " 
~Philosophical ~' 8 1 ~77 , l - 20. 

responses 

More on Deductive 
and Inductive 
Arguments 

Trudy Govier 
Trent University 

The existence of confusing material in 
textbooks has not been enough to convince 
Samuel Fohr that the distinction between in-
duct i ve and deductive arguments should be re-
linqu ished. (.See "The Deductive- Inductive 
Distinction", Informal ·Logic Newsletter, 
ii . 2 . ) Fohr proposes, fol owing a definition 
in Olson ' s Meaning and Argument, that the 
distinction betweenef.eductive and inductive 

7 

arguments be established on the grounds of 
the intentions of the person putting forward 
the argument. Arguments , he says, are 
people's arguments; they are put forward in 
order to convince other people. People may 
intend either that their arguments provi de 
conclusive reasons for what they are t rying 
to demonstrate, o r that they provi de less 
than conclusive reasons. In the fi r st case , 
an a r guer ' s intentions establish his argument 
as deductive . In the second case , they make 
it inductive . A desirable conse quence of 
this approach is that it provides for both 
good and bad arguments in each category. 
Most of the time, Fohr thinks, we are able t o 
tell what an arguer's i ntentions are, or wer e 
If we cannot , we must judge the argument 
"both ways ". 

This proposal does not strike me as v e ry 
satisfactory . I am surprised that Fohr, who 
says that he cannot accept "purportedly valid 
as a definition of 'deductive argument ' , can 
rest content with an appea l to intention here 
I have the following difficulties with his 
proposal: 

1. Either there will be evidence for the 
arguer's intentions regarding conclusiveness 
in the wording of his argument, or there wi l l 
not. In the fi r s t case, intentions and 
"purported validity" or "involving a claim to 
validity" (Copi) will amount to much the same 
thing . There are numerous examples, as Fohr 
admits, where wo r ding is not helpful. After 
all, conclusiveness in the sense of logical 
entailment is a philosopher's concept, and 
even such English words as "must" , "there-
fore", and "shows conc l usively" will not 
prov ide a reliable basis for inferring that 
the arguer is claiming conclusiveness in the 
sense that the premises are supposed to 
lo~ically ential the conclusion . If, on the 
ot er hand, we seek to avoid these difficul-
ties with wording--making the author's ~a~so 
and that alone the criterion for determ~n~ng 
his intention- -we will find ourselves unable 
to apply the distinction to many cases where 
authors are dead or absent. This is absurd 
if the inductiye/deductive distinction is 
supposed to be a fundamental tool in the 
assessment of argument . We can , of course, 
look at the indeterminate arguments "both 
ways", as Fohr suggests; but the more ofte n 
we do this, the more often we are bound to· 
wonder why all of logic should have been 
erected around this fuzzy distinction in the 
first place. 

2 . If we really take Fohr seri ously on the 
over- riding importance of intention, then we 
will have to accept the peculiar consequence 
that there are inductive arguments which a r e 
deductively valid, and deductive arguments 
which are inductively strong. For instance , 
suppose someone argues: 

l. Either Levesque wil l be defeated at 
the next election, or he will win 
and call another refer endum . 

2. Since Quebecers are fond of Levesque , 
he will not be defeated at the ne xt 
election. 

3. Thus, there will in all likelihood 
be another referendum. 

This argument is deductively valid, but the 
conclusion contains the tentative expression 
"in all likelihood". If the arguer is a 



logically untutored person, he may deem him-
self to have provided only some good reasons 
for thinking there will be another referendum; 
he may not realize that his statements con-
tain a perfect disjunctive syllogism, which, 
of course, is deductively valid. (A perfect-
ly sensible reason for such a person to take 
this view would be the fact that the first 
premise is by no means certain; sensing this, 
one might express his conclusion hesitantly.) 
Thus the intention will be 'inductive', des-
pite the fact that the argument is deductive-
ly valid. This consequence seems counter-
intuitive. Fohr might reply that we can as-
sess an inductive argument by deductive cri-
teria, and conversely, but: (a) his stress 
on intention suggests that he would not move 
in this direction, and (b) if he did, that in 
itself would cast doubt on the importance of 
the inductive/deductive distinction for 
practical criticism. If a deductive argument 
can be assessed by inductive standards, or an 
inducti ve argument by deductive standards, 
what is the point in calling th~ deductive 
or inductive in the first place? 

3. Ordinary language is not nearly as strict 
wi th words like "conclusive" "shows", or even 
~deduce" as is philosophical and logical 

tradition. I think that this may be the ex-
planation for Conan Doyle's description of 
Sherlock Holmes as a great master of deduc-
tion. We sometimes use "deduce" loosely 
enough so that it means more or less what is 
meant by "infer" or "conclude from". I might, 
in that sense, deduce from your irritable 
d i sposition that you are tired today. I 
doubt that Conan Doyle ever meant to claim 
that Holmes's conclusions followed with 
logical necessity from the bits of evidence 
he had. 

Now I do not wish to propose here that or-
dinary language is entirely all right and 
that philosophers and logicians have been 
guilty of a pernicious distortion of it. The 
problem for Fohr is that the traditional no-
tion of deductive logical validity or--as he 
puts it--conclusiveness or necessarr implica-
tion is one wh~ch philosophers and ogicians 
have constructed. It requires, first, a 
concept of logically necessary connection, 
and second, a distinction between considera-
tions of truth and those of the connection 
between the premises and the conclusion of an 
argument. All of us know from teaching ex-
perience that it can be very difficult to con-
vey these notions to philosophically untu-
tored people; in fact, some never succeed in 
grasping them. Who is missing something here 
--us, or them? As a philosopher who values 
my own education, I am of course inclined to 
think they are, but in view of the doubts of 
Duhem, Quine, Waismann, and others, there are 
some grounds for scepticism here. If argu-
ers' intentions are to provide the basis for 
·a distinction between deductive and inductive 
arguments which will be anything like the 
traditional one, those arguers will have to 
formulate their intentions with a knowledge 
of the difference between logical and empir-
ical connection, and the distinction between 
considerations of truth and those of validity. 

Now Fohr, like others. interested in infor-
mal logic, wants to attend to real arguments 
put forward by real people. This means not 

8 

only philosophers and logicians writing text-
books, but politicians, lawyers, housewives, 
historians, economists, psychologists, and 
others. Fohr says that the reason the induc-
tive/deductive distinction should be pre-
served is that arguers should know whether 
they intend to offer conclusive tin the 
logician's sense) reasons for their claims, 
or not. But in view of the background which 
such intentions require, I am not sure that 
this is an entirely reasonable norm for the 
arguing public. Even if it is, the world at 
present is far from being in a condition 
where it could be realized. ~ost people who 
are out there constructing arguments do not 
have an acquaintance with. logic and philosophy. 
And as far as the logical/contingent aspect 
of the necessary background is concerned, 
philosophers do not have a sufficient con-
sensus on this matter to launch an education 
program for the general public. 

Despite all of this, I confess that there 
is something in me which shares Fohr's re-
luctance to scrap the distinction between in-
ductive and deductive argumen~s. This reluc-
tance may be purely the product of caution 
and education; one naturally hesitates to 
think that a distinction which has been 
around for so long, and around which so much 
teaching of logic has been organized, could 
simply be ill-founded. Those with doubts 
may be missing something--but what is it? 
Not, I would argue, a norm for arguers' 
intentions. 

Referring to a suggestion of Carl Wellman's 
which I forwarded to the editors of the News-
letter in 1979, Fohr remarks that he can see 
no good reason to have more than two cate-
gories of argument. I do not wish to commit 
myself to Wellman's concept of a "conductive 
argument", but contra Fohr, I can see a rea-
son for moving to more than two categories. 
(In categorizing one will, of course, have to 
ask what the categories are for, and their 
purpose should have something to do with how 
many we need.) The common modern sense of 
'inductive' is so broad that all non-conclu-
sive arguments are classified as inductive 
and hence in the same category. Yet induc-
tive logic deals exclusively with the confir-
mation/disconfirmation of empirical hypotheses 
by empirical data on particulars. Now this 
combination of definition and focus can make 
people think that all arguments are either 
deductive or scientific-empirical-inductive. 

Such a belief we inherit from positivism, 
and it is this legacy which makes people 
think that there cannot be arguments in sup-
port of moral judgements. The broad modern 
sense of induction found in, say, Copi and 
more or less endorsed by Fohr will leave the 
"inductive" category as a grab-bag holding 
everything from legal arguments, consequen-
tialist moral or prudential reasoning, and 
scientific confirmation to philosophers' 
paradigm case arguments, transcendental argu-
ments, and infinite regress arguments. To 
say that an a.rgument is inductive in the 
broad modern s·ense tells us virtually nothing 
about it and it is for this reason, I think, 
that the move to more than the two categories 
would be tempting. 

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