The following is an excerpt from Stephen Toulmin's The Uses of Argument (Cambridge University Press, 1958). It is intended to emphasize the importance of buttressing one's opinions with data and justification.

The Pattern of an Argument: Data and Warrants

"What, then, is involved in establishing conclusions by the production of arguments?" Can we, by considering this question in a general form, build up from scratch a pattern of analysis which will do justice to all the distinctions which proper procedure forces upon us? That is the problem facing us.

Let it be supposed that we make an assertion, and commit ourselves thereby to the claim which any assertion necessarily involves. If this claim is challenged, we must be able to establish it-that is, make it good, and show that it was justifiable. How is this to be done? Unless the assertion was made quite wildly and irresponsibly, we shall normally have some facts to which we can point in its support: if the claim is challenged, it is up to us to appeal to these facts, and present them as the foundation upon which our claim is based. Of course we may not get the challenger even to agree about the correctness of these facts, and in that case we have to clear his objection out of the way by a preliminary argument: only when this prior issue or 'lemma', as geometers would call it, has been dealt with, are we in a position to return to the original argument. But this complication we need only mention: supposing the lemma to have been disposed of, our question is how to set the original argument out most fully and explicitly. 'Harry's hair is not black', we assert. What have we got to go on? we are asked. Our personal knowledge that it is in fact red: that is our datum, the ground which we produce as support for the original assertion. Petersen, we may say, will not be a Roman Catholic: why?: we base our claim on the knowledge that he is a Swede, which makes it very unlikely that he will be a Roman Catholic. Wilkinson, asserts the prosecutor in Court, has committed an offence against the Road Traffic Acts: in support of this claim, two policemen are prepared to testify that they timed him driving at 45 m.p.h. in a built-up area. In each case, an original assertion is supported by producing other facts bearing on it.

We already have, therefore, one distinction to start with: between the claim or conclusion whose merits we are seeking to establish (C) and the facts we appeal to as a foundation for the claim-what I shall refer to as our data (D). If our challenger's question is, 'What have you got to go on?', producing the data or information on which the claim is based may serve to answer him; but this is only one of the ways in which our conclusion may be challenged. Even after we have produced our data, we may find ourselves being asked further questions of another kind. We may now be required not to add more factual information to that which we have already provided, but rather to indicate the bearing on our conclusion of the data already produced. Colloquially, the question may now be, not 'What have you got to go on?', but 'How do you get there?'. To present a particular set of data as the basis for some specified conclusion commits us to a certain step; and the question is now one about the nature and justification of this step.

Supposing we encounter this fresh challenge, we must bring forward not further data, for about these the same query may immediately be raised again, but propositions of a rather different kind: rules, principles, inference-licences or what you will, instead of additional items of information. Our task is no longer to strengthen the ground on which our argument is constructed, but is rather to show that, taking these data as a starting point, the step to the original claim or conclusion is an appropriate and legitimate one. At this point, therefore, what are needed are general, hypothetical statements, which can act as bridges, and authorize the sort of step to which our particular argument commits us. These may normally be written very briefly (in the form 'If D, then C'); but, for candour's sake, they can profitably be expanded, and made more explicit: 'Data such as D entitle one to draw conclusions, or make claims, such as C', or alternatively 'Given data D, one may take it that C.'

Propositions of this kind I shall call warrants (W), to distinguish them from both conclusions and data. (These 'warrants", it will be observed, correspond to the practical standards or canons of argument referred to in our earlier essays.) To pursue our previous examples: the knowledge that Harry's hair is red entitles us to set aside any suggestion that it is black.' (The very triviality of this warrant is connected with the fact that we are concerned here as much with a counter-assertion as with an argument.) The fact that Petersen is a Swede is directly relevant to the question of his religious denomination for, as we should probably put it, 'A Swede can be taken almost certainly not to be a Roman Catholic.' (The step involved here is not trivial, so the warrant is not self-authenticating.) Likewise in the third case: our warrant will now be some such statement as that 'A man who is proved to have driven at more than 30 m.p.h. in a built-up area can be found to have committed an offence against the Road Traffic Acts.'

The question will at once be asked, how absolute is this distinction between data, on the one hand, and warrants, on the other. Will it always be clear whether a man who challenges an assertion is calling for the production of his adversary's data, or for the warrants authorising his steps? Can one, in other words, draw any sharp distinction between the force of the two questions, 'What have you got to go on?' and 'How do you get there?'? By grammatical tests alone, the distinction may appear far from absolute, and the same English sentence may serve a double function: it may be uttered, that is, in one situation to convey a piece of information, in another to authorise a step in an argument, and even perhaps in some contexts to do both these things at once. (All these possibilities will be illustrated before too long.) For the moment, the important thing is not to be too cut-and-dried in our treatment of the subject, nor to commit ourselves in advance to a rigid terminology. At any rate we shall find it possible in some situations to distinguish clearly two different logical functions; and the nature of this distinction is hinted at if one contrasts the two sentences, 'Whenever A, one has found that B' and 'Whenever A, one may take it that B.'

We now have the terms we need to compose the first skeleton of a pattern for analysing arguments. We may symbolise the relation between the data and the claim in support of which they are produced by an arrow, and indicate the authority for taking the step from one to the other by writing the warrant immediately below the arrow:

As this pattern makes clear, the explicit appeal in this argument goes directly back from the claim to the data relied on as foundation: the warrant is, in a sense, incidental and explanatory, its task being simply to register explicitly the legitimacy of the step involved and to refer it back to the larger class of steps whose legitimacy is being presupposed.

This is one of the reasons for distinguishing between data and warrants: data are appealed to explicitly, warrants implicitly. In addition, one may remark that warrants are general, certifying the soundness of all arguments of the appropriate type, and have accordingly to be established in quite a different way from the facts we produce as data. This distinction, between data and warrants, is similar to the distinction drawn in the law-courts between questions of fact and questions of law, and the legal distinction is indeed a special case of the more general one...(The Uses of Argument pp. 97-100).

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