 Two other issues central to this debate are that the key concept “natural” seems ambiguous in many different ways (see Hume 1751, App. 3; Mill 1874; Brennan [1988] 2014; 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 anlogy with gardening has sometimes been used to explore the nature of restoration (Allison 2004).