Modern day lexical databases are not constructive, but differential (Miller et al 1990).We outline the logical structure of the task of a conceptual analyst who wishes to construct a constructive lexicon based on a Universal Theory Model of Concepts.Elementary notions of descriptive and explanatory adequacy are developed within this model.The diverse streams of evidence available for the conceptual analyst to engage in empirical inquiry are reviewed in the domains of light and perception. Theories for Constructive LexiconsMajor projects have been conducted for centuries to record, in one form or another, representations of word meanings.This has been in the form of the lexicographer's dictionary or the more modern computational linguist's electronic databases (WordNet, FrameNet, Verb-Net) e.g. last year's symposium (Miller, Fillmore, Palmer, Lenat and Hayes 2004).The degree to which computational linguists and cognitive scientists draw upon these resources as accurate descriptions of lexical knowledge is astonishing.Researchers speak of "putting meaning in your trees", providing "deep semantics", automatically labeling "semantic roles", or using Word-Net as the authority for word sense disambiguation, to name some key projects.(Palmer et al 2002, Fillmore et al 2001, Gildea and Jurafsky 2002) Given the increasing reliance to these databases, it may appear that the terms meaning and semantic are not being used glibly and that the theoretical foundations of these databases were sound.Even the most cursory analysis shows that this is not so.Consider the distinction made by the originators of WordNet between a constructive vs. differential lexicon: In a differential theory of the lexicon, meanings can be represented by any symbols that enable a theorist to distinguish among them; In a constructive theory of the lexicon, the representation should "contain sufficient information to support an accurate construction of the concept (by either a person or a machine)" (Miller et al 1990).Today's dictionaries and all of today's lexical databases are differential: the intension of synsets of WordNet are just sufficient so that someone who already knows English can distinguish among synsets, while the thematic roles used in VerbNet and FrameNet are notoriously difficult to define: primitive terms such as Agent,