La Logique ou L`Art de penser - No

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La Logique ou L’Art de penser
The work La Logique ou L’Art de penser, which is also known by the name
Logic of Port Royal, came out anonymously in Paris in 1662. Both Jansenists
Antoine Arnauld and Pierre Nicole are considered to be authors. The logic
of Port Royal, which was the centre of Jansenism, was very influential up to
our time and shaped science and therewith reasoning significantly.
The logic of Port Royal follows the Cartesian ideal of science, which is largely
based on mathematics. For representation, axioms, definitions and proofs
were chosen. The Logique is based on the causal world picture introduced
by Descartes and continues the ”modern rationalism” founded by him. Two
types of ”knowledge” are distinguished from one another:
• the scientific knowledge, which is absolute and is based on the evidence
of rationality and
• the probable knowledge, which is ”only believed” to be true.
Therefore, a division into the area of science takes place, in which everything
is ”certain” or ”true”, and into the inferior area of belief, in which everything
is only ”probable”.
Probability refers to the past and is illustrated by means of religious traditions, historical events and the genuineness of documents.
The problem arises whether ”probability” or rather ”moral certainty” can be
associated with (completed) facts, so that one can decide to believe in them
(“se déterminer à la croire”).
As a check, ”external reasons” (authorities) and ”internal reasons” (surrounding circumstances) are considered. A particular cursory objectification
of the approach was effectuated by the proposal of a kind of probability logic
primarily for the latter.
In the last chapter of the Logique, the decision problem with regard to uncertainty is considered, where future advantages and disadvantages are weighed
up. As illustrations, the authors use the calculation of games of chance and
present an example of how chances and risks can be rationally weighed up
”in the way of geometry” and put into relation to each other.
“Il ne faut pas seulement considérer le mal et le bien en soi,
mais aussi la probabilité qu’il arrive ou n’arrive pas, & regarder
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Géometriquement la proportion que toutes ces choses ont ensemble.”
As an illustration, a lottery is used and the ”expected profit” is computed
as a decision-making aid.