Ideas from 'Against the Professors' by Sextus Empiricus [180], by Theme Structure

[found in 'The First Philosophers' (ed/tr Waterfield,Robin) [OUP 2000,0-19-282454-6]].

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3. Truth / A. Truth Problems / 5. Truth Bearers
It is only when we say a proposition that we speak truly or falsely
                        Full Idea: It is only when we say a proposition that we speak truly or falsely.
                        From: Sextus Empiricus (Against the Professors [c.180], 8.74)
                        A reaction: This makes assertions truth-bearers, rather than propositions. But a proposition can be true or false if it is stamped with a date and/or place. "Shakespeare was born in Stratford on 23rd April 1664". No one needs to assert that.
5. Theory of Logic / E. Structures of Logic / 1. Logical Form
'Man is a rational mortal animal' is equivalent to 'if something is a man, that thing is a rational mortal animal'
                        Full Idea: Definitions are identical to universal propositions in meaning, and only differ in syntax, for whoever says 'Man is a rational mortal animal' says the same thing in meaning as whoever says 'If something is a man, that thing is a rational mortal animal'.
                        From: Sextus Empiricus (Against the Professors [c.180], 11.8)
                        A reaction: How strikingly like Bertrand Russell's interest and solutions. Sextus shows a straightforward interest in logical form, of a kind we associate with the twentieth century. Did Sextus Empiricus invent quantification?
14. Science / A. Basis of Science / 1. Observation
How can you investigate without some preconception of your object?
                        Full Idea: A preconception and conception must precede every object of investigation, for how can anyone even investigate without some conception of the object of investigation?
                        From: Sextus Empiricus (Against the Professors [c.180], 8.331a)
                        A reaction: The Duhem-Quine thesis about the 'theory-ladenness of observation' is just a revival of some routine ancient scepticism. As well as a conceptual scheme to accommodate the observation, there must also be some motivation for the investigation.
23. Ethics / B. Contract Ethics / 9. Contractualism
Right actions, once done, are those with a reasonable justification
                        Full Idea: Right action is whatever, once it has been done, has a reasonable justification.
                        From: Sextus Empiricus (Against the Professors [c.180], 7.158)
                        A reaction: Why does he add 'once it has been done'? Wouldn't a proposed action be right if it had a reasonable justification? This grows out of the classical and Stoic emphasis on reason in ethics, and leads towards Scanlon's Contractualism.
26. Natural Theory / A. Speculations on Nature / 4. Mathematical Nature
The tektraktys (1+2+3+4=10) is the 'fount of ever-flowing nature'
                        Full Idea: The tektraktys (1+2+3+4=10) is the 'fount of ever-flowing nature', because nature is a harmony of three concords (4th,5th and octave), and these ratios (4:3, 3:2, and 2:1) are found in the tektraktys.
                        From: Sextus Empiricus (Against the Professors [c.180], 7.95)