Abstract. — One of Herman Cappelen’s main arguments for the importance of conceptual engineering is the Master Argument, which proceeds from the claim that our words and concepts might have better meanings than the ones they have, and argues on these grounds that we ought to try to improve what we mean.  I present some metasemantic views on which the premise that meanings might be better is true but there is no possibility of conceptual engineering, show why the Master Argument fails in these cases, and relate the discussion to theoretical choice points for the metasemantic view I favour: temporal externalism, according to which what we mean now is determined in part by what happens later.