In philosophy, theories of welfare’s nature abound. One of these is Canadian moral philosopher L.W. Sumner’s (subjective) ‘happiness theory of welfare’, which he argues in his 1996 book ‘Welfare, Happiness, and Ethics’ (or ‘WHE’ for short) is “the best available … about the nature of welfare” (WHE, 184). Since its publication, Sumner’s theory of welfare has attracted a range of criticisms, such that it is now widely (though I would argue wrongly) regarded as falling well short of being “the best available”. This paper contends that criticisms of Sumner’s ‘happiness theory of welfare’ misinterpret or misunderstand the welfare theoretic system presented in WHE (explicated here in terms of that system’s implicit as well as explicit details). The totality of the implicit and explicit details of Sumner’s welfare theoretic system is ‘what Sumner’s really saying in WHE’ about welfare’s nature, which is more detailed and ‘determined’ than is currently appreciated in the philosophical literature. This paper lays the groundwork for a reappraisal (in a follow-up paper) of Sumner’s ‘happiness theory of welfare’ as a viable candidate for “the best available theory” of welfare’s nature.