Individual natural entities (whether sentient or not, living or not), Andrew Brennan (1984) argues, are not designed by anyone to fulfill any purpose and therefore lack “intrinsic function” (i.e., the function of a thing that constitutes part of its essence or identity conditions). This, he proposes, is a reason for thinking that individual natural entities should not be treated as mere instruments, and thus a reason for assigning them intrinsic value. Furthermore, he argues that the same moral point applies to the case of natural ecosystems, to the extent that they lack intrinsic function. In the light of Brennan’s proposal, Eric Katz (1991 and 1997) argues that all natural entities, whether individuals or wholes, have intrinsic value in virtue of their ontological independence from human purpose, activity, and interest, and maintains the deontological principle that nature as a whole is an “autonomous subject” which deserves moral respect and must not be treated as a mere means to human ends. Carrying the project of attributing intrinsic value to nature to its ultimate form, Robert Elliot (1997) argues that naturalness itself is a property in virtue of possessing which all natural things, events, and states of affairs, attain intrinsic value. Furthermore, Elliot argues that even a consequentialist, who in principle allows the possibility of trading off intrinsic value from naturalness for intrinsic value from other sources, could no longer justify such kind of trade-off in reality. This is because the reduction of intrinsic value due to the depletion of naturalness on earth, according to him, has reached such a level that any further reduction of it could not be compensated by any amount of intrinsic value generated in other ways, no matter how great it is.

As the notion of “natural” is understood in terms of the lack of human contrivance and is often opposed to the notion of “artifactual”, one much contested issue is about the value of those parts of nature that have been interfered with by human artifice — for instance, previously degraded natural environments which have been humanly restored. Based on the premise that the properties of being naturally evolved and having a natural continuity with the remote past are “value adding” (i.e., adding intrinsic value to those things which possess those two properties), Elliot argues that even a perfectly restored environment would necessarily lack those two value-adding properties and therefore be less valuable than the originally undegraded natural environment. Katz, on the other hand, argues that a restored nature is really just an artifact designed and created for the satisfaction of human ends, and that the value of restored environments is merely instrumental. However, some critics have pointed out that advocates of moral dualism between the natural and the artifactual run the risk of diminishing the value of human life and culture, and fail to recognize that the natural environments interfered with by humans may still have morally relevant qualities other than pure naturalness (see Lo 1999). Two other issues central to this debate are that the key concept “natural” seems ambiguous in many different ways (see Hume 1751, App. 3, and Brennan 1988, Ch. 6, Elliot 1997, Ch. 4), and that those who argue that human interference reduces the intrinsic value of nature seem to have simply assumed the crucial premise that naturalness is a source of intrinsic value. Some thinkers maintain that the natural, or the “wild” construed as that which “is not humanized” (Hettinger and Throop 1999, p. 12) or to some degree “not under human control” (ibid., p. 13) is intrinsically valuable. Yet, as Bernard Williams points out (Williams 1992), we may, paradoxically, need to use our technological powers to retain a sense of something not being in our power. The retention of wild areas may thus involve planetary and ecological management to maintain, or even “imprison” such areas (Birch 1990), raising a question over the extent to which national parks and wilderness areas are free from our control. An important message underlying the debate, perhaps, is that even if ecological restoration is achievable, it might have been better to have left nature intact in the first place.