The neurological examination is the second great organizing tool. Where many specialties treat the physical exam as confirmation, neurology often uses it as diagnosis. Focal weakness with upper motor neuron signs localizes to the brain or spinal cord; a peripheral pattern with distal sensory loss and diminished reflexes suggests neuropathy; a fluctuating fatigable weakness tips toward a neuromuscular junction disorder. Small, subtle asymmetries or the presence of specific signs — clonus, extensor plantar responses, sensory level, gaze palsies, cerebellar dysmetria — convert vague complaints into anatomical hypotheses. Patten-style teaching underlines systematic examination: map deficits anatomically first, then seek disease processes that fit that map.