This paper addresses the synergy and antagonism between symptoms and signs among 2,914 elderly Canadians diagnosed in 15 categories, including no cognitive impairment, cognitive impairment but no dementia, mild, moderate and severe forms of Alzheimer's disease and vascular dementia, 4 subtypes of possible Alzheimer's disease, Parkinson's dementia, unspecified other dementias and unclassified dementias Attention is paid to the relationships between symptoms and signs rather than conventional analyses which assume independent signs. We demonstrate that dementia progression and specific aetiologies have characteristic patterns of decline and destruction from the strong synergy that exists between symptoms and signs among the population with no cognitive impairment. These findings have potential implications for the incorporation of new diagnostic criteria into existing databases.