In the present paper, I discuss two main objections raised by Professor T. Koizumi (in " Philosophy " vol 60. 1972) against corresponding two themes in my previous article ' Micro-ethics and Macroethics' ("Philosophy" vol 58, 1971). Professor Koizumi's first objection is against so-called ' ecological explanation of man' which I had advocated in my proposal of Macro-ethics. He argues that the ecological explanation will be justifiable when it is applied to the explanation of the behaviour of plants and animals but will not be so when it is applied to the explanation of human behaviour. The ecological explanation of human beings will not be able to account for the existence of human morality just because methodologically it treats human beings as a species of animals and conscequenty as subject to biological laws such as 'struggle for existence' or 'natural selection'. 'To adopt this mode of explanation,' he says, 'is to look human beings 'pulled down to the level of lower animals'. It seems, however, that the objection of Professor Koizumi is apparently based on his emotional reaction against 'biological explanation of man' and has no rational ground whatever. My second point is about his objection against my theme which says that value or ought propositions in their original form will be made (not deduced in formal logical sense) from the body of fact proporitions of different levels, thereby obeying laws which do not belong to that of formal logic or so-called practical syllogism. Here I think Professor Koizumi had missed my real point. What I intended to clarify was not formal logical validity of practical syllogism nor that of ethical discourse in general containing value or ought proposition. My real problem was to explain how value or ought propositions, in their origin, come to function by making use of various kinds of factual knowledge including conscious fact propositions as well as unconscious dispositions like habit or natural directedness. My main concern was an investigation into the origin of our ethical discourse in general. I also wish to point out, against Professor Koizumi's criticism, that the really important problem in ethics should not be just finding and following, salva veritate, some formal validity of ethical discourse, but lies, rather, in analysing and constructing a model of the emergence of value or ought propositions from discourses which do not contain value or ought propositions.