EVANS, Gillian R.

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138
PROBABILIS AND PROVIN G
Probabile pluris modis dicitur, says the author of the Summa
Sophisticorum Elenchorum ' He has in mind the many degree s
of probability, from what seems probable to everyone, to wha t
seems probable only to the individual of exceptional percepti-
veness . His notion of probability is, however, confined to th e
sense which is by far the most usual in twelfth century
authors : what is probable is what ` seems likely . 2 But a
second sense of probabilis was in use ; in certain key passages i t
is important that probabilis should be rendered as ` provable ' i f
we are to understand the author's intention .
Nicholas of Amiens speaks of : probabiles . . . fidei nostrae
rationes in his De Arte Catholicae Fidei 3 and Alan of Lille
states in his Contra Haereticos that ` where there is neither
authority nor reason, there is no provable opinion ' : ubi autem
nec adest auctoritas, nec ratio, non est probabilis opinio. 4 Both
these writers of the last decades of the twelfth century were
addressing themselves to the problem of demonstrating th e
truth of the Christian faith to unbelievers . Nicholas concluded
that only reason afforded a proof which everyone woul d
accept, for the heretics deliberately distorted authorities, inter-
preting them to suit their own ends, or else they simply refuse d
to accept them . 5 Alan thought it necessary to try to meet th e
heretics on their own ground by presenting them with authori-
ties which would contradict their own. 6 But both were concer-
ned with ` proving ', with the ` provability ' of Christian truths ,
and it is in this sense that they use probabilis in these passages .
1. Logica Modernarum ed . L. M. de Rijk (Assen 1967) I p . 273 .22. See
Introduction on the dating of this treatise .
2. Ibid . p
. 276 .1-2 .
3. P. L . 210 .596, and see ALAIN DE LILLE, Textes inédits, ed .
M . T
. d'Alverny, Paris, 1965, p . 68-9, on the question of authorship .
4. P. L. 210 .317, and see Textes inédits p. 156-62 on this work .
5. P
. L . 210 .596 .
6. P. L . 210 .307-8 .
139
By far the greater part of twelfth century discussions o f
probability concentrate upon the distinction between what i s
probably true and what is necessarily true . Peter Abelard, fo r
example, remembers that William of Champeaux, or some
other master he has heard, believed that the truth of a hypo-
thetical proposition might consist in necessity or only in proba-
bility. He reflects upon the idea that what is probable is that
which has an appearance of truth, that which is easily conce-
ded by anyone who hears it ; he suggests that probability con-
cerns what seems to be so, while truth refers to what really i s
so . He concludes that ` probable conclusions ' cannot be treate d
in the same way as `necessary' ones .' Adam of Balsam
touches on probability, too, and he,too, takes probabilis to
means `probable' or `likely' . Probabilia falsi similia non sun t ,
he comments, in a paraphrase of the ubiquitous notion tha t
what is probable is verisimilis . 8 In a commentary on the Peri-
hermemias of the School of Peter Abelard, in a discussion o f
proportion, it is said to be ` probable ' that if four things are i n
proportion, and two of them bear the same relation to on e
another as the other two, then the second will be to the fourt h
as the first to the third . 9 In all these discussions, probability
has a good deal of positive force ; what is probable is certainly
not unlikely to be true ; but a probable conclusion is certainly
not envisaged as a conclusion proved, finally and necessarily .
The root meaning of ` probable ' is there, however : argu-
mentum est ratio probans aliquid ; 10 an argument is a reason
which ` proves ' something, insists the author of the Excerpta
Norimbergensia . Adam of Balsam has a clear idea of the tw o
senses of probabilis. ` Something probable ' is that to whic h
` one may easily consent' ; or it is that ` for which there is a
sufficient argument' (quia ei facile consentitur ; quia ad id satis
argumenti), II The difference is spelt out at length in a
7. PETRUS ABAELARDUS, Dialectica, ed . L . M . de Rijk (Assen 1956) p. 272 .
8. ADAM BALSAMNIENSIS, Twelfth Century Logic I, ed . L. Minio-Paluell o
(Rome 1956) p . 14.5, cf. p . 78 .16.
9. Abelardiana Inedita, ed . L . Minio-Paluello, Twelfth Century Logic II ,
Rome, 1958, paragraph 246 .
10. Logica Modernorunt II", Excerpta Norimbergensia. p . 119 .13 .
11. Twelfth Century Logic . I, p . 39 .7-8, cf. p . 39.16 .
140
fragment of a Perihern7enias commentary from the school o f
Alberic of Rheims, the Frustula Logicalia : the author draws a
parallel between ` visible ' and ` probable ' . Just as we say that
what is ` visible ' is what can be seen (visibile dicitur quod potest
videri), so we say that what is ` provable ' is what can be pro-
ved (esse probabile quod probari potest) . Therefore we can say
that both the statements :
This argument is probable
and :
This argument is not probabl e
are true . If we take probabilis to mean, on the one hand, ` That
is probable which can be proved ', we can say that this argu-
ment is not probable, for many things are evident (evidentia )
which cannot be proved ; if we take probabilis to mean likely ,
we can say that the same argument is probable . 12 The diffe-
rence between the two meanings of probabilis could scarcely be
made plainer .
When, then, Nicholas of Amiens says that we must look fo r
` probable reasons for our faith ' or Alan of Lille speaks of a
` probable ' opinion, there is no reason to suppose that they
mean merely a `likely' reason or opinion . They have in min d
something much stronger and more precise, a meaning of th e
word probabilis which is germane to the discussions of the late
twelfth century on the ways in which the truth of the Christian
faith may be proved to the unbeliever . The less common sens e
of probabilis is therefore of the first importance in such con -
texts, and if we are not alert to the usage we are in danger o f
misunderstanding at least two significant statements of prin-
ciple in this area .
Bristol
	
Gillian R . EVAN S
12 . Logica Modernorum. I, p. 61 . The editor has had to supply gaps here ,
but there can be no doubt of the correctness of his emendations .


"Probabilis" and Proving

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