For example, Prof. Pigou in the Economics of Welfare (4th ed. p. 127) writes ( my italics):
"Throughout this discussion, except when the contrary is expressly stated, the fact that some resources are generally unemployed against the will of the owners is ignored. This does not affect the substance of the argument, while it simplifies its exposition."
Thus, whilst Ricardo expressly disclaimed any attempt to deal with the amount of the national dividend as a whole, Prof. Pigou, in a book which is specifically directed to the problem of the national dividend, maintains that the same theory holds good when there is some involuntary unemployment as in the case of full employment.