From Paradiso Canto XIII (109 starting), with Charles Singleton’s (prose) translation. I’ve checked the several commentaries I have on hand and a number of others through Dartmouth’s Dante Project and can’t find a single line addressing the possible origins or background of the metaphor chi pesca per lo vero e non ha l’arte, only explanations of the metaphor itself. It feels so biblical but I guess I’ve just always assumed a reference on relation to ‘fishers of men’ and the like. I’ve included at bottom Singleton’s gloss on the philosophers and, for curiosity, Cristoforo Landino’s painfully detailed explanation of the metaphor from his 1481 commentary.
E questo ti sia sempre piombo a’ piedi,
per farti mover lento com’ uom lasso
e al sì e al no che tu non vedi:ché quelli è tra li stolti bene a basso,
che sanza distinzione afferma e nega
ne l’un così come ne l’altro passo;perch’ elli ‘ncontra che più volte piega
l’oppinïon corrente in falsa parte,
e poi l’affetto l’intelletto lega.E di ciò sono al mondo aperte prove
Parmenide, Melisso e Brisso e molti,
li quali andaro e non sapëan dove;Vie più che ‘ndarno da riva si parte,
perché non torna tal qual e’ si move,
chi pesca per lo vero e non ha l’arte.
And let this ever be as lead to your feet, to make you slow, like a weary man, in moving either to the yes or the no which you see not; for he is right low down among the fools, alike in one and in the other case, who affirms or denies without distinguishing, because it happens that oftentimes hasty opinion inclines to the wrong side, and then fondness for it binds the intellect. Far worse than in vain does he leave the shore (since he returns not as he puts forth) who fishes for the truth and has not the art. And of this Parmenides, Melissus, Bryson, are open proofs to the world, as are the many others who went on but knew not whither.
The philosophers:
Parmenide: Parmenides, an early Greek philosopher, was born at Elea in Italy ca. 513 B.C. He is the chief representative of the Eleatic philosophy, in which he was followed by his disciple Zeno; he and Zeno, according to Plato, met Socrates in Athens in ca. 448 B.C. Parmenides wrote in verse his philosophical views On Nature, of which only fragments are extant. Melisso: Melissus, a philosopher of Samos who flourished ca. 441 B.C., was a follower of Parmenides. Only fragments of his writings are extant. Brisso: Bryson was a Greek philosopher mentioned by Aristotle as having attempted to square the circle, a problem which apparently he tried to solve dishonestly by non-geometrical methods (Soph. elench. I, 11, 171b; Anal. post. I, 9, 75b).
And Landino:
Viè più che ‘ndarno: la sententia è questa: possiamo dire che uno sia arriva, quando anchora non ha pensato se la chosa è vera o no; ma quando comincia a investigare, allhora si parte da riva et entra nel fiume. Adunque chome el pescatore se si parte da riva et non ha l’arte del pescare nè anchora gli strumenti apti si parte indarno per che non pigla, chosì chi si mette a investigare el vero sanza dialectica et philosophia et senza le scientie che gle ne possono mostrare s’affaticha indarno. Ma è anchora peggio perchè oltra al perdere la faticha, entra nello errore nel quale non era prima. Adunque è peggio che ‘l pescatore, perchè lui non piglando torna tale quale si partì. Ma chostui torna in piggior grado perchè ha falsa opinione la quale non havea prima.
Extracts 