 Relations of influence between variables are often encoded in formal models. Just as the causal relations between tokens and types can be either deterministic or probabilistic, so too can the relations of influence between variables be either deterministic or probabilistic. Deterministic relations between variables are represented with structural equations models; whereas indeterministic relations between variables can be represented with probabilistic models (sometimes with structural equations models with random errors—see the entry on  causal models—or  often with just a causal graph paired with a probability distribution over the values of the variables appearing in that graph—see the entry on  probabilistic causation.)