Abstract

Objections to longtermism often focus on issues like fanaticism, discounting, or classic reasons to doubt the tractability of positively influencing the far future. I argue that another challenge has been underdiscussed relative to those—namely, that posed by unawareness: many of the long-term possibilities most relevant to our actions are unknown to us. I develop this challenge by introducing the notion of determinative unawareness, where unknown outcomes are decisive for whether an action is overall positive or negative. Greaves and MacAskill’s responses—treating unawareness as ordinary uncertainty or appealing to catchall states—do not, by themselves, suffice, as it is far from clear how they can avoid arbitrariness. Importantly, I argue that existing cases outlining the relative robustness of some longtermist strategies, such as option value maximization, do not ultimately succeed in sidestepping determinative unawareness. I then discuss two broad ways one could relax the normative views supporting the longtermist thesis to rescue some version of longtermism from the grip of unawareness, and suggest that they face serious limitations.

1. Introduction

Longtermism, the view that the impact of our actions on the far future is of particular moral importance (MacAskill 2022; Ord 2020; Greaves & MacAskill 2025),^[1] has raised a wide variety of criticisms (Greaves & MacAskill 2025). Prominent examples include arguments for discounting, in some manner, the interest of future beings (see Mogensen 2022; Setiya 2014; Nordhaus 2007; 2008; Curran 2025; Riedener 2025), classic intractability objections (see Thorstad 2025a, §4; Tarsney 2023), the objection from fanaticism (see Bottomley & Williamson 2025; Tarsney 2020; Beckstead 2013, §6)^[2], and that from infinite paralysis (see Tarsney & Wilkinson 2025). Alongside such critiques, the academic literature also counts numerous defenses of the longtermist thesis against these. Both critiques and defenses appear in Greaves et al.’s (2025) recent collection, Essays on longtermism. The most salient assumptions behind the longtermist view seem to have all been well discussed at this point.

Taking stock, here are six claims we might or might not agree on about longtermism:^[3]

Even if one assumes the world will plausibly end very soon, such that there may not be any

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On Cluelessness