Combining Philosophers

Ideas for Peter Geach, Gottfried Leibniz and Robert Hanna

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6 ideas

10. Modality / D. Knowledge of Modality / 1. A Priori Necessary
Truths of reason are known by analysis, and are necessary; facts are contingent, and their opposites possible [Leibniz]
     Full Idea: There are two kinds of truths: of reasoning and of facts. Truths of reasoning are necessary and their opposites impossible. Facts are contingent and their opposites possible. A necessary truth is known by analysis.
     From: Gottfried Leibniz (Monadology [1716], §33)
Intelligible truth is independent of any external things or experiences [Leibniz]
     Full Idea: Intelligible truth is independent of the truth or of the existence outside us of sensible and material things. ....It is generally true that we only know necessary truths by the natural light [of reason]
     From: Gottfried Leibniz (Letters to Queen Charlotte [1702], 1702)
     A reaction: A nice quotation summarising a view for which Leibniz is famous - that there is a tight correlation between necessary truths and our a priori knowledge of them. The obvious challenge comes from Kripke's claim that scientists can discover necessities.
Proofs of necessity come from the understanding, where they have their source [Leibniz]
     Full Idea: The fundamental proof of necessary truths comes from the understanding alone, and other truths come from experience or from observations of the senses. Our mind is capable of knowing truths of both sorts, but it is the source of the former.
     From: Gottfried Leibniz (New Essays on Human Understanding [1704], 1.01)
     A reaction: Interesting because it not only spells out that necessary truths are known a priori, but also explicitly says that the understanding is the 'source' of the truths, or at least the source of their proofs. He also says possibilities derive from essences.
10. Modality / D. Knowledge of Modality / 2. A Priori Contingent
Only God sees contingent truths a priori [Leibniz]
     Full Idea: Only God sees contingent truths a priori.
     From: Gottfried Leibniz (On Freedom [1689], p.95)
     A reaction: This because everything is interconnected, and the whole picture must be seen to understand a contingent truth.
If we understand God and his choices, we have a priori knowledge of contingent truths [Leibniz, by Garber]
     Full Idea: Insofar as we have some insight into how God chooses, we can know a priori the laws of nature that God chooses for this best of all possible worlds. In this way, it is possible to have genuine a priori knowledge of contingent truths.
     From: report of Gottfried Leibniz (Conspectus libelli (book outline) [1678], A6.4.1998-9) by Daniel Garber - Leibniz:Body,Substance,Monad 6
     A reaction: I think it would be doubtful whether our knowledge of God's choosings would count as a priori. How do we discover them? Ah! We derive God from the ontological argument, and his choosings from the divine perfection implied thereby.
10. Modality / D. Knowledge of Modality / 4. Conceivable as Possible / c. Possible but inconceivable
What we cannot imagine may still exist [Leibniz]
     Full Idea: It does not follow that what we can't imagine does not exist.
     From: Gottfried Leibniz (Letters to Johann Bernoulli [1699], 1698.11.18)
     A reaction: This just establishes the common sense end of the debate - that you cannot just use your imagination as the final authority on what exists, or what is possible.