My personal and brief view of the above notions is also included in many other entries in CEO.SIGNS (what) are objective perceptions by our senses.
SIGNALS (thought) are subjective and represent our understanding of signs. Clinical and family histories are sources of signals – are not signs unless validated by our own observations.
SYNDROME (cluster) refers to non-random cluster of signs-signals combinations.
PATHOGENESIS (how) – the most fundamental and complex notion in Medicine – the “mechanism” or process of expression of causes.
DIAGNOSIS (synthesis) – unifying label for the above amplified by the natural history (chronology, evolution, epidemiology) or prognosis.