This is true whether content properties are reducible to NP properties or supervene on them. It states that that causal relations supervene on mechanisms. Chronic psychoses can supervene many years later, based on myxoedema, hypoglycaemia or Addisonian crisis. Others maintain that higher-order properties simply supervene over lower levels without direct causal interaction. When the "Yin" and the "Yang" are at variance, calamitous changes supervene. This is interpreted as meaning that mental events supervene upon the physical. In biological systems phenotype can be said to supervene on genotype.