As conservation professionals who value natural landscapes for the many benefits they provide, we wholeheartedly agree with nearly all the advice offered by Noss et al.(2012). They encourage conservation professionals to work toward maintaining or restoring connectivity across large landscapes; to focus attention on the greatest threat to biological diversity, namely land-use change in response to human population growth; to demonstrate the value of nature to humans; and to popularize the idea that continental-level conservation can be achieved. We encourage conservation scientists who share the beliefs implicit in Noss et al.’s advice to direct effort toward these worthwhile activities. We are troubled, however, by Noss et al.’s misleading conflation of value-based judgments and scientific judgments. Specifically, we find fault with the main arguments that Noss et al. offer to support their target of protecting at least 50% of a region to meet goals for conserving biological diversity. They say this target is based on “best available science... the research and expert opinion of scientists... scientific studies and reviews” and “a strict scientific point of view.” These statements are deceptive because all conservation targets are ultimately based on normative value judgments (Svancara et al. 2005; Wilhere 2008).

Conservation assessments, such as those cited in Noss et al., use empirical data and usually employ site-selection algorithms, population viability analysis, or both. They produce evidence-based, scientific results for particular conservation goals or objectives, such as the level of representation for each species or an acceptable level of extinction risk, which are personal value-based judgments.