From material conditions to action
Marx adds the idea that actions affect the world.  Recall this passage from The Eighteenth Brumaire:
"Man makes his own history, but he does not make it out of the whole cloth; he does not make it out of conditions chosen by himself, but out of such as he finds close at hand. The tradition of all past generations weighs like an alp upon the brain of the living. At the very time when men appear engaged in revolutionizing things and themselves, in bringing about what never was before, at such very epochs of revolutionary crisis do they anxiously conjure up into their service the spirits of the past, assume their names, their battle cries, their costumes to enact a new historic scene in such time-honored disguise and with such borrowed language
And so, action or practice is implicated as a part of the materialist side but it is an ACTIVE not a passive element.