Brake system for a vehicle, having a master brake cylinder; a brake medium reservoir; a first brake circuit assigned to exactly one wheel and having a first wheel brake cylinder which is hydraulically connected to the master brake cylinder, via a first switching valve arranged between the master brake cylinder and the first wheel brake cylinder, in such a way that a first brake medium volume can be displaced out of the master brake cylinder through the at least partially opened first switching valve into the first wheel brake cylinder, and having a first pump which is assigned to the first wheel brake cylinder, wherein, by means of a first wheel inlet valve of the first brake circuit, a displacement of brake medium from the first switching valve to the first wheel brake cylinder and/or from a delivery side of the first pump to the first wheel brake cylinder can be controlled, and, by means of a first wheel outlet valve of the first brake circuit, a displacement of brake medium from the first wheel brake cylinder to a suction side of the first pump can be controlled; a second brake circuit assigned to exactly one wheel and having a second wheel brake cylinder which is hydraulically connected to the master brake cylinder, via a second switching valve arranged between the master brake cylinder and the second wheel brake cylinder, in such a way that a second brake medium volume can be displaced out of the master brake cylinder through the at least partially opened second switching valve into the second wheel brake cylinder, and having a second pump which is assigned to the second wheel brake cylinder, wherein, by means of a second wheel inlet valve of the second brake circuit, a displacement of brake medium from the second switching valve to the second wheel brake cylinder and/or from a delivery side of the second pump to the second wheel brake cylinder can be controlled, and, by means of a second wheel outlet valve of the second brake circuit, a displacement of brake medium from the second wheel brake cylinder to a suction side of the second pump can be controlled; and a third brake circuit decoupled from the master brake cylinder and assigned to exactly two wheels (16a and 16b) and having - a third pump coupled to the brake medium reservoir; - a third wheel brake cylinder and a fourth wheel brake cylinder which are hydraulically connected to the third pump in such a way that a third brake medium volume can be pumped by means of the third pump from the brake medium reservoir via a third wheel inlet valve into the third wheel brake cylinder and a fourth brake medium volume can be pumped by means of the third pump from the brake medium reservoir via a fourth wheel inlet valve into the fourth wheel brake cylinder; and - a continuously adjustable valve via which the third pump is hydraulically connected to the brake medium reservoir such that a displacement of brake medium from the third pump into the brake medium reservoir can be controlled by means of the continuously adjustable valve; - wherein a fifth brake medium volume can be displaced through a third wheel outlet valve from the third wheel brake cylinder into the brake medium reservoir and a sixth brake medium volume can be displaced through a fourth wheel outlet valve from the fourth wheel brake cylinder into the brake medium reservoir; characterized by an isolating valve connected to the brake medium reservoir; wherein the first pump is hydraulically connected to the isolating valve, by means of a first check valve, such that a seventh brake medium volume can be pumped by means of the first pump through the at least partially opened isolating valve and the first check valve into the first wheel brake cylinder; and wherein the second pump is hydraulically connected to the isolating valve, by means of a second check valve, such that an eighth brake medium volume can be pumped by means of the second pump through the at least partially opened isolating valve and the second check valve into the second wheel brake cylinder; and wherein the brake system has exactly twelve actuable valves (30a, 30b, 36a, 36b, 50a, 50b, 90, 106, 116a, 116b, 132a, 132b) comprising the first and second switching valve (30a, 30b), the first to fourth wheel inlet valve (36a, 36b, 116a, 116b), the first to fourth wheel outlet valve (50a, 50b, 132a, 132b), the continuously adjustable valve and the isolating valve, which can be controlled at least into an open state and into a closed state by means of an electrical signal provided by a control device of the brake system. - a third pump coupled to the brake medium reservoir; - a third wheel brake cylinder and a fourth wheel brake cylinder which are hydraulically connected to the third pump in such a way that a third brake medium volume can be pumped by means of the third pump from the brake medium reservoir via a third wheel inlet valve into the third wheel brake cylinder and a fourth brake medium volume can be pumped by means of the third pump from the brake medium reservoir via a fourth wheel inlet valve into the fourth wheel brake cylinder; and - a continuously adjustable valve via which the third pump is hydraulically connected to the brake medium reservoir such that a displacement of brake medium from the third pump into the brake medium reservoir can be controlled by means of the continuously adjustable valve; - wherein a fifth brake medium volume can be displaced through a third wheel outlet valve from the third wheel brake cylinder into the brake medium reservoir and a sixth brake medium volume can be displaced through a fourth wheel outlet valve from the fourth wheel brake cylinder into the brake medium reservoir;