I've never understood Marx to be a liberal, even a philosophical one & I take him to be a good figure for marking a substantial break w/ liberalism toward establishing a particularly Left politics. A primary reason for this, emphasizing the "philosophical", is how freedom works https://twitter.com/BenBurgis/status/1254046965412900865
For one, liberals take an essentializing view of human nature on which they establish rights & the right to property is always a primary focus of liberal politics. But Marx's materialism breaks w/ this - a reason why Sartre sees "existence preceding essence" already in Marx
Property is a right primarily to secure our freedom against the freedom of others. From Hobbes to Locke to Kant, the freedom of others is a limitation on our own freedom & Kant is perhaps the most explicitly clear on this point. Certainly, a paradigmatic liberal thinker
The view rests on a metaphysics of human nature that places our freedom outside of material conditions. For Kant, in the noumenal. But Locke is there too. One of Locke's arguments for God concerns the impossibility of deriving free consciousness from unconscious matter.
So, human nature is grounded in a quasi-theological & supernatural realm beyond the bounds of historical material forces. Part of Marx's anti-essentializing move is to have human beings be partially molded by the material conditions in which they live in a reciprocal relation
For Marx, human freedom is not a supernatural property of the will that must be secured in the material world against the freedom of others which threaten it. Instead, freedom is only realized *through* the freedom of others - an basically anti-liberal position, philosophically.
Part of the reason is that under liberalism, w/ its emphasis on private property, the material conditions encourage competition under a zero-sum logic where my freedom is realized only by the denial of another's freedom. I am secure only by denying you.
But Marx rejects this & it is the philosophical underpinning of his ultimate criticism of private property & why private property is to be abolished as freedom is encouraged.
Freedom is only realized under material conditions of non-competition wherein the basic needs of each is provided for such that they can pursue their free ends without being captured by a wage system in which their freedom is commodified as labor for sale
That Marx views freedom as a basic feature of living in community is not sufficient to make him a liberal. We find this requirement in Plato's Republic, in Socrates' image of the soul from Book IX for example, & throughout Aristotle, & we can hardly call them "liberals"
Marx's concept of freedom under dialectical materialism is sufficiently different from liberalism to establish a philosophic break w/ liberalism. Sure, this can read as "continuous", but that's toothless since any critical response is "continuous" with that to which it responds.