Another recent review of the same book:

Nothing Personal: How ideas made Derek Parfit - https://news.ycombinator.com/item?id=38494017 - Dec 2023 (26 comments)

Related:

Derek Parfit: The Perfectionist at All Souls - https://news.ycombinator.com/item?id=35688300 - April 2023 (21 comments)

How to Be Good: The Philosopher Derek Parfit (2011) - https://news.ycombinator.com/item?id=22037240 - Jan 2020 (6 comments)

Why anything? Why this? (1998) - https://news.ycombinator.com/item?id=13315746 - Jan 2017 (77 comments)

Derek Parfit has died - https://news.ycombinator.com/item?id=13304873 - Jan 2017 (38 comments)

How to Be Good: Derek Parfit's Moral Philosophy - https://news.ycombinator.com/item?id=11273495 - March 2016 (16 comments)

Reasons and Persons is a truly mind-expanding book. It's the opposite of the cliché of analytic philosophy as arid word games.

Having just read the book, I will say this review seems spot on in its assessment. It’s a good but not great read, approachable and a good story, but thin on philosophical insight.

Thinner than it could be

> Those who don’t buy the jigsaw puzzle view of humanistic thought are unlikely to be convinced by Parfit’s ingenious version of moral monism. After all, why should we think that all genuine human ideals and values, such as equality, freedom, justice and compassion, must form part of some pre-ordained or constructible harmonious whole? The evidence would suggest otherwise: that is, that an irreducible conflict of ethical ideals and values is the unalterable human situation (past and present). Monists like Parfit perceive the undeniable fact of moral disagreement as an avoidable state of affairs and one that can be eliminated through the application of human reason. And moral monists also tend to believe, as Parfit unequivocally did, that the only coherent form of moral realism is moral monism ‑ in other words, that the only alternative to the view that there is a single, true morality is moral relativism, or its unblushing first cousin, moral nihilism, the philosophical view which denies the existence and possibility of objective moral values.

I'm concerned that the reviewer, Johnny Lyons, is erroneously conflating what _is_ (descriptive) from what _should_ be (normative). Parfit surely recognizes what exists, descriptively; his project involves motivating a normative ethics.

This criticism is so obvious (to philosophers at least) that I wonder if I'm missing something and/or misinterpreting Lyons.

I understood Lyons as driving at a related point of Parfit getting too deep into theoretic analytic philosophy and being a little too ambitious or carried away with reconciling irreducible frameworks and values, which is tangential to your point around the difference between ought and is.