Authors/Ockham/Summa Logicae/Book III-4/Chapter 15

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Latin English
CAP. 15. DE FALLACIA PETITIONIS PRINCIPII.
Post fallacias penes quas peccant argumenta peccantia in forma dicendum est de fallaciis penes quas non peccant argumenta sophistica, sed penes quas peccat opponens in arguendo contra respondentem. Quarum prima est petitio principii, quae tunc accidit quando opponens, quamvis inferat conclusionem quam intendit, tamen non potest convincere respondentem, eo quod accipit quod deberet probare. After the fallacies where the arguments are erroneous in form, we must speak of fallacies where the sophistical arguments are not erroneous, but where the opponent is in error against the respondent. Of which the first is ‘begging the question’, which happens when the opponent, although he infers the conclusion which he intends, nevertheless cannot refute the respondent, because he accepts what ought to be proved.
Et dicitur `petitio principii' non quia accipit illud idem quod deberet inferre, tunc enim nulla esset apparentia, sed dicitur opponens petere principium quando accipit aeque ignotum vel ignotius illo quod deberet inferre. And it is called ‘begging the question’ not because he accepts that same thing which ought to be inferred, for then nothing would be apparent, but rather the opponent is said to beg the question when he accepts what is equally unknown, or more unknown than that which ought to be inferred.
Et propter hoc semper potest respondens petere probationem assumpti quousque accipiat aliquid notius. And because of this the respondent can always seek a proof of what is assumed until he accepts something more known.
Fit autem ista fallacia multis modis. Uno modo fit quando arguitur a nomine synonymo ad synonymum; sicut sic arguendo `Marcus currit, igitur Tullius currit'. This fallacy can happen in many ways. It happens in one way when it is argued from a synonymous name to a synonym, for example in arguing ‘Mark runs therefore Tully runs’.
Statim enim accipitur aliquid aeque ignotum cum conclusione inferenda. For immediately there is accepted something as equally unknown as the conclusion to be inferred.
Alius modus est quando arguitur a definitione exprimente quid nominis ad definitum vel e converso. Et hoc quia in omni disputatione debent praesupponi significata vocabulorum. Unde patet quod hic est petitio principii `ignis est productivus caloris, igitur ignis est calefactivus'. Alius modus est quando arguitur ab una convertibili propositione ad aliam, quarum neutra est prior vel notior alia; sicut hic `nullus musicus est grammaticus, igitur nullus grammaticus est musicus'. Unde universaliter quando assumitur aeque ignotum vel ignotius ipsi respondenti quam sit conclusio inferenda, est petitio principii. Sciendum est tamen quod quamvis respondens non possit convinci per rationem dum accipitur aeque ignotum vel ignotius, potest tamen convinci per auctoritatem, si velit auctoritatem recipere. Sicut si respondens nolens negare auctoritatem aliquam, neget istam `Marcus currit', quamvis opponens sic arguat `Tullius currit, igitur Marcus currit' non convincet eum; si tamen ostendit istam `Tullius currit' in auctore quem non vult negare, convincet eum sufficienter. Another way is when it is argued from a nominal definition to what is defined, or conversely. And this is because in every disputation the significates of the words (vocabulorum) ought to be presupposed. Hence it is clear that 'fire is productive of heat, therefore fire is calefactive' is begging the question.[1] Another way is when it is argued from one convertible proposition to another, of which neither is prior or better known than the other, for example 'no musical thing is skilled in grammar, therefore nothing skilled in grammar is a musical thing'. Hence universally when it is assumed what is equally unknown, or more unknown to that respondent than the conclusion to be inferred, there is begging of the question. It should be known that although the respondent could not be refuted by reasoning while he accepts what is equally unknown or more unknown, yet he may be refuted by authority, if he wishes to receive the authority. For example, if the respondent, not wishing to deny some authority, denies 'Mark runs', although the opponent argues 'Tully runs, therefore Mark runs', the opponent does not refute him. But if if he shows 'Tully runs' in some author which he does not wish to deny, he refutes him sufficiently.
Et ita est de aliis. And so it is in other [cases].

Notes

  1. i.e. because 'productive of heat' and 'calefactive' are synonyms
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