How we cite our quotes: (Chapter.Section.Paragraph) or (Chapter.Paragraph)
Quote #1
When we leave this sphere of simple circulation or the exchange of commodities, which provides the 'free-trader vulgaris' with his views, his concepts and the standard by which he judges the society of capital and wage-labour, a certain change takes place, or so it appears, in the physiognomy of our dramatis personae. He who was previously the money-owner now strides out in front as a capitalist; the possessor of labour-power follows as his worker. The one smirks self-importantly and is intent on business; the other is timid and holds back, like someone who has brought his own hide to market and now has nothing else to expect but—a tanning. (6.23)
Most of the time in Das Kapital, Marx thinks of the capitalist and the worker as impersonal forces: capital and labor-power. But here he lets go a bit and describes them as people. In contrast to the views of pop economists who promoted capitalism—the free-trader vulgaris—Marx sees the relationship as one of power, where the capitalist dominates the worker and is able to tan him (abuse him). That's because the capitalist owns the means of production, whereas the worker can only sell his labor-power.
Quote #2
The fact that half a day's labour is necessary to keep the worker alive during 24 hours does not in any way prevent him from working a whole day. Therefore the value of labour-power, and the value which that labour-power valorizes in the labour-process, are two entirely different magnitudes; and this difference was what the capitalist had in mind when he was purchasing the labour-power [...] What was really decisive for him was the specific use-value which this commodity possesses of being a source not only of value, but of more value than it has itself. (7.2.22)
With the means of production owned, the capitalist is in the powerful position of being able to hire a commodity that can produce value. Meanwhile, the worker is that lowly producer, overpowered. Marx saw this relationship and advocated the overthrow of capitalism in the Communist Manifesto.
Quote #3
The capitalist maintains his rights as a purchaser when he tries to make the working day as long as possible, and, where possible, to make two working days out of one. On the other hand, the peculiar nature of the commodity sold implies a limit to its consumption by the purchaser, and the worker maintains his right as a seller when he wishes to reduce the working day to a particular normal length. There is here therefore an antinomy, of right against right, both equally bearing the seal of the law of exchange. Between equal rights, force decides. Hence, in the history of capitalist production, the establishment of a norm for the working day presents itself a a struggle over the limits of that day, a struggle between collective capital, i.e. the class of capitalists, and collective labour, i.e. the working class. (10.1.8)
In the perfectly functioning, ideal capitalism Marx describes, the contract between the capitalist and the worker is a one in which each party is on equal legal footing. So their rights, being equal, don't decide who gets to call the shots over the length of the working day. What decides is force—that is, power. The stronger party gets to determine the length of the working day. Capitalists are stronger in that they own the means of production, but workers are stronger in that they are greater in number.