I am surprised that we have no entries from Hegel, Fichte, or Heidegger, noted for their why-say-it-in-eight-words-when-sixty-are-available tendencies.
But to my knowledge, the longest sentence written by a philosopher is the following 309-word original from the pen of John Locke:
“It having been shewn in the foregoing discourse,
1. That Adam had not, either by natural right of fatherhood, or by positive donation from God, any such authority over his children, or dominion over the world, as is pretended:
2. That if he had, his heirs, yet, had no right to it:
3. That if his heirs had, there being no law of nature nor positive law of God that determines which is the right heir in all cases that may arise, the right of succession, and consequently of bearing rule, could not have been certainly determined:
4. That if even that had been determined, yet the knowledge of which is the eldest line of Adam’s posterity, being so long since utterly lost, that in the races of mankind and families of the world, there remains not to one above another, the least pretence to be the eldest house, and to have the right of inheritance:
All these premises having, as I think, been clearly made out, it is impossible that the rulers now on earth should make any benefit, or derive any the least shadow of authority from that, which is held to be the fountain of all power, Adam’s private dominion and paternal jurisdiction; so that he that will not give just occasion to think that all government in the world is the product only of force and violence, and that men live together by no other rules but that of beasts, where the strongest carries it, and so lay a foundation for perpetual disorder and mischief, tumult, sedition and rebellion, (things that the followers of that hypothesis so loudly cry out against) must of necessity find out another rise of government, another original of political power, and another way of designing and knowing the persons that have it, than what Sir Robert Filmer hath taught us.”
That is the opening sentence of Locke’s Second Treatise of Government. It makes one yearn for more, which one can find here.
I am open to argument about the archaic punctuation. If we take the end of Locke’s fourth numbered point as a full stop, then the passage breaks down to one 156-word chunk and another 153-word chunk.
But absent further argument and contributions, I declare Locke the winner.
(Subject to further discoveries that would bump him down in the rankings.)