Mechanism model is a model that describes and explains phenomena or processes. It explains the emergence and development of phenomena by establishing the correlation between variables. The mechanism model usually pays attention to the relationship between variables and causal mechanism, but does not try to provide an explanation of causal relationship. For example, suppose there is a mechanism model to describe the relationship between temperature and weather. The model can show that there is a correlation between temperature rise and weather warming, but it is not certain that temperature rise is the causal factor leading to weather warming.
Causality model is a model to describe and explain causality. It not only pays attention to the relationship between variables, but also tries to infer and explain causality. Causality model is usually based on reasoning and empirical analysis of causality, which can verify and predict causality. For example, suppose there is a causal model to explain the relationship between smoking and lung cancer. The model can show that smoking is a cause of lung cancer.
So the difference between mechanism model and causal model lies in whether it provides explanation and inference of causal relationship. The mechanism model pays attention to the relationship between variables, while the causal model not only pays attention to the relationship, but also tries to infer and explain the causal relationship.