A new theoretical framework for understanding and working with the dementing illnesses of old age is presented, and explicated with particular reference to senile dementia of the Alzheimer type. For several reasons the commonly accepted model, which assumes a simple linear causal relationship between neuropathology and dementia, is inadequate. A more comprehensive model, grounded in a monistic view of the mind-brain relationship, must take into account not only the psychological states that correspond to particular brain states, but also both developmental and pathological aspects of brain structure. Using this we can describe the dementing process, ‘normal’ psychological functioning in old age, pseudodementia and ‘benign senescent forgetfulness’. Further, the scope for some degree of ‘rementia’ is explored.