What kind of theory is Marx's labour theory of value?

Marx starts from the &s;stylised fact&s; that under capitalism, in contrast to all other modes of production, human labouring activity appears in an estranged or alienated form. It appears in the form of the products this labouring activity produces, namely commodities as values. The labour theory of value (LTV) should, by contrast, be the kind of theory that is qualitative in nature and rooted in the causal-explanatory mode of theorisation because, unencumbered by pursuing inappropriate objectives, and possessing explanatory power, this kind of theory leads, ultimately, to relevance. Marxist economic theory is replete with &s;toy&s; models, a little elaboration will pay dividends. Whilst Karl Marx never really elaborated upon the notion of abstraction, others have, and the need to take abstraction seriously is widely recognised in Marxist circles – it is just ignored when the deductive mode of theorisation is employed to formulate quantitative versions of the LTV.