1. Method for identifying a chemical substance from a set of output states provided by a chemical sensor array being exposed to the chemical substance, the method comprising steps for selecting from a set of class descriptions for different chemical substances a first class description and one or more further class descriptions, whereby the first class description is related to a first chemical substance and a further class description is related to a further chemical substance, estimating a first likelihood value and one or more further likelihood values, whereby the first likelihood value represents a probability that the set of output states corresponds to the first class description, and a respective further likelihood value represents a probability that the set of output states corresponds to a respective further class description, determining from the estimated first and further likelihood values the class description with the highest likelihood value, characterised in that an estimation of a first and further likelihood value combines the likelihood values estimated for at least two subsets of the set of output states corresponding to the first and further class description, respectively.