Logic of Real Arguments by Alec Fisher | Excerpt

The following excerpt about analyzing arguments is from Professor Alec Fisher's The Logic of Real Arguments.

The key ideas we need to introduce for the moment are ‘conclusion’, ‘reason’ and ‘establish’. The passages in which we are interested all contain reasoning, they are all arguing a case. We argue a case by presenting grounds or reasons for accepting some conclusion (which need not come at the ‘end’ of the passage of course!) and the reasons are put forward in order to establish the conclusion, to justify it, prove it, support it, demonstrate it – or some such word...[F]or the present we want to rely on, and draw out, the reader’s logical intuitions.

Of course the interesting question is always whether the reasons given do justify the conclusion, but it is impossible to answer that question until you have identified the conclusion and the reasons presented for it...

The general form of the exercise is the same in each case...[T]he reader should first say whether it is an argument (whether it contains reasoning to a conclusion). For those which are arguments the reader should next say what their conclusion is, and then what reasons are given for that conclusion. Finally the reader should attempt to decide whether the reasoning establishes its conclusion in each case. It is important of course to say why you reach your decision.

Example (1)
If the money supply were to increase at less than 5% the rate of inflation would come down. Since the money supply is increasing at about 10% inflation will not come down. 

This clearly is a piece of reasoning. It is the sort of argument which has been all too familiar in Britain in recent years, but, discounting this, the use of the word ‘since’ shows that what we have here is reasoning. The conclusion is,

inflation will not come down 

and the reasons given are,

if the money supply were to increase at less than 5% the rate of inflation would come down 


the money supply is increasing at 10%.

This reasoning does not establish its conclusion: the reasons could both be true and the conclusion false. Something else could bring inflation down – for example a fall in the price of imports. There is nothing in the argument as it is presented to suggest that only a reduction in the rate of increase of the money supply will bring down inflation. Many people...construe this as a good argument..., but it isn’t...[I]t is an example of a classical logical fallacy.

The Logic of Real Arguments, 2nd Edition, by Alec Fisher
Copyright © 2004 Alec Fisher.  Reprinted with the permission of Cambridge University Press.


  1. Denying the antecedent

  2. The only valid conclusion one could draw, in respect to the first premise, is that since inflation will not come down, the supply of money is not increasing at a rate lower than 5%. Of course, this doesn't prove that it's rate is 10% or 20% or anything of the sort, but just that, since inflation is not descreasing, then therefore the sufficient condition in the first sentence is not possible.

  3. Actually, no. "Inflation" means inflation-of-the-money-supply. Price inflation (inflation-of-prices-at-market) is completely different and is not entirely directly related. So the statement can't be declared false on those grounds.

    It's a common mistake, though.

    1. "Inflation" refers to price-inflation, unless otherwise noted, throughout economic discourse (http://www.clevelandfed.org/research/Commentary/1997/1015.pdf). Monetary inflation, what you refer to as "inflation-of-the-money-supply," is, in any case, largely believed to indeed be "directly related" to price inflation: An increase in money supply, all else equal, effects an increase in price levels (http://pareto.uab.es/schoi/p4_eng.pdf).

  4. Actually it looks like the author is also confusing the terms...

  5. Premise: MS<5% => decrease Inflation
    Premise: increase 10 % (not MS<5% )
    Conclusion: not decrease inflation. invalid! (mistaken negation).

  6. In the realm of the LSAT, the argument's truthfulness is not to be questioned but rather the validity of the argument.

    OK Statement: if money supply is increasing at less than 5%, inflation might go down. Money supply is increasing at 10%, therefore rate of money supply is not affecting rate of inflation decrease.

    vs what this argument says:

    The KEY words that cause it to be false are "WILL NOT GO DOWN".

    "Money supply rate is not at 5% therefore NOTHING will cause inflation to decrease."

    The scope is too extreme in stating something WILL NOT HAPPEN - the premises do not justify this argument.