discussion 

Vol. VIII. 3, Fall 1986 
I nformal Logic 

Inconsistency: A Fallacy? 

JULIAN WOLFE 

One of the informal fallacies dis-
cussed by Blair and Johnson in their 
text Logical Self-Defense is that of 
inconsistency.[1] No doubt there are 
some forms of inconsistency which are 
clearly correct to describe as fallacious. 
For example, if either the premises 
of an argument contradict one another, 
explicitly or implicitly, or a premise or 
what it entails or presupposes and the 
conclusion do so, then the argument is 
undermined in that not all the state-
ments contained in it can be true . 

However the authors claim that a 
fallacy of in~onsistency may occur when 
there is an inconsistency between 
what a person preaches and what that 
person practices. Since by "fallacy" 
they mean "a violation of one of the 
criteria which govern good argu-
ments," [2] one presumes that it is in 
the context of argument that the 
fallacy of inconsistency might arise. 
Indeed, the authors say as much: 

It is not a fallacy to assert inconsistent 
statement or to behave inconsistently 
with one's pronoucements. The fallacy 
occurs only when inconsistency of one 
sort or another undermines an argu-
ment.[3] 

So if a mother tells her teenage son 
that he should not smoke, and does so 
herself, there is an inconsistency, but 
no fallacy unless she gives the teenager 
reasons why he should not smoke, 
i.e., argues for her viewpoint. 

The question I pose is how inconsis-

Carleton University 

tency between assertion and action can 
undermine an argument and thus 
constitute a fallacy. If the mother tells 
her son that he should not smoke 
because it is harmful to his health as 
well as that of other children in the 
family who are forced to inhale the 
fumes second hand, how are these 
reasons shown not to be good reasons if 
the mother herself smokes? 

Inconsistency between preaching and 
practice can be evidence of addiction 
("I know I shouldn't smoke but I just 
can't quit"), selfishness (" I keep 
telling myself to give more to charity 
but I really like new clothes and tra-
vel"), or weakness ("I feel guilty 
about my infidelities, but I'm not 
strong enough to always resist tempta-
tion"). The reasons one offers in op-
position to smoking and adultery, or 
in favour of charity, may be good ones 
even if one doesn't always practice 
what one preaches. People don't 
always live up to their convictions, 
but their convictions may be defensible 
and defended with good reasons . 

Blair and Johnson give the example 
of Canadian officials who exhort 
Canadians to winter vacation at home, 
while vacationing themselves during 
the winter in Florida and the Carib-
bean. We are asked to imagine the 
following argument made by the 
officials to persuade Canadians to take 
winter holidays in Canada.[4] 



152 

(a) To help Canada ' s balance-of-
payments position, as many 
Canadian dollars should be 
kept in the country as possible, 

(b) The Canadian economy would 
benefit from increased spending 
in our winter tourism and 
entertainment industries, 

(c) So Canadians should spend their 
winter holiday money at home in 
Canada . 

Given the inconsistency between the 
preaching and practice of these offi-
cials, shall we conclude that the above 
argument commits a fallacy of incon-
sistency? How does their behaviour 
undermine the argument? Does it 
show that (a) and (b) are not good 
reasons for (c) or don't adequately 
support it? Surely not . Blair and John-
son go on to say: 

Yet many of these same officials who 
vacationed in Florida and the Caribbean 
must have been operating on some such 
principle as the following: 

PR: It is not imperative that Cana-
dians spend their winter holiday money 
at home in Canada(5). 

Their point is that the behaviour of 
these officials indicates they accept a 
principle that contradicts the conclusion 
(c) . 

However, in the first place , PR is 
neither entailed nor presupposed by 
either (a) or (b), and hence there is no 

Inconsistency 

inconsistency, within the argument 
itself. The argument is not undermin-
ed. Second, the officials needn't be 
assumed to be operating on PRo They 
may be simply be failing to live up to 
their own convictions. After all, warm 
weather is very attractive to Canadians 
during our cold winters, and too 
tempting for some to resist. Charged 
with inconsistency, our officials may 
just admit to acting wrongly. 

I suggest that to charge inconsistency 
as a fallacy in such cases is itself to 
commit a fallacy, a type of ad hominem . 
I ts form form is: 

He doesn't practice what he preaches 
So, he can ' t adequately defend what 
he preaches 

or 
What he preaches is mistaken . 

Notes 

[1] R.H . Johnson and J.A. Blair, 
Logical Self-Defense (McGraw-
Hill Ryerson, 1983, 2nd edition, 
pp.59-63. 

[2] Ibid, p . 33 
[3] Ibid., P. 60. 
[4] Ibid., p. 61 . 
[5] Ibid ., p. 61. 

Professor Julian Wolfe, Department 
of Philosophy, Carleton University, 
Ottawa, Ontario K1S 586 0