Catalyst

A property, event or material substance that must be present to synthesize or produce some other property, event or material substance without becoming part of the result of the process. In chemistry, catalysts speed up or slow down a chemical reaction without undergoing permanent chemical change thereby. An example of a catalyst in society is the justice of peace or the priest who is necessary to legalize a marriage but does not himself participate in it. The assembly of a machine according to information carrying instructions is another example. (Krippendorff)