Read "Capital, Volume One: The Process of Production of Capital" by Karl Marx online for free on Textopian. Full text with search, annotations, highlights, and AI-powered reading aids.
The various factors of the labour-process play different parts in forming the value of the product.
The labourer adds fresh value to the subject of his labour by expending upon it a given amount of additional labour, no matter what the specific character and utility of that labour may be. On the other hand, the values of the means of production used up in the process are preserved, and present themselves afresh as constituent parts of the value of the product; the values of the cotton and the spindle, for instance, re-appear again in the value of the yarn. The value of the means of production is therefore preserved, by being transferred to the product. This transfer takes place during the conversion of those means into a product, or in other words, during the labour-process. It is brought about by labour; but how?