The first requirement of productive labour, therefore, is that it is productive of a commodity, and that the labour does not consume more commodities than it produces, i.e. that it produces more value than it costs.
“By producing commodities the productive worker constantly reproduces the variable capital which he constantly consumes in the form of wages. He constantly produces the fund which pays him, “which maintains and employs him”.” (p 164)
Under capitalism, all production is based upon co-operative labour, and this co-operation increases in proportion as the division of labour separates each type of production into more and more tasks and types of labour. In previous modes of production, the worker combined mental and manual labour. They created a mental image of the product to be created, before engaging in its production, and performed all of the other functions of administration etc. required to purchase material and so on. Under capitalism, these mental labours themselves become separated off as separate tasks, and forms of labour, which are equally required for production as manual labour. In determining the types of labour required for the production of commodities, therefore, Smith includes all of these types of labour.
“Adam Smith naturally includes in the labour which fixes or realises itself in a vendible and exchangeable commodity all intellectual labours which are directly consumed in material production. Not only the labourer working directly with his hands or a machine, but overlooker, engineer, manager, clerk, etc.—in a word, the labour of the whole personnel required in a particular sphere of material production to produce a particular commodity, whose joint labour (co-operation) is required for commodity production. In fact they add their aggregate labour to the constant capital, and increase the value of the product by this amount.” (p 164)
As an aside here, Marx asks,
“How far is this true of bankers, etc.?” (p 164)