Specified complexity

The Intelligent Design concept of specified complexity was developed by mathematician and philosopher William Dembski. Dembski claims that when something exhibits specified complexity (i.e., is both complex and specified, simultaneously) one can infer that it was produced by an intelligent cause (i.e., that it was designed), rather than being the result of natural processes (see naturalism). He provides the following examples: "A single letter of the alphabet is specified without being complex. A long sentence of random letters is complex without being specified. A Shakespearean sonnet is both complex and specified." He states that details of living things can be similarly characterized, especially the "patterns" of molecular sequences in functional biological molecules such as DNA.

Dembski defines a probability of 1 in 10150 as the "universal probability bound". Its value corresponds to the inverse of the upper limit of "the total number of possible specified events throughout cosmic history," as calculated by Dembski. He defines complex specified information (CSI) as specified information with a probability less than this limit. (The terms "specified complexity" and "complex specified information" are used interchangeably.) He argues that CSI cannot be generated by the only known natural mechanisms of physical law and chance, or by their combination. He argues that this is so because laws can only shift around or lose information, but do not produce it, and chance can produce complex unspecified information, or non-complex specified information, but not CSI; he provides a mathematical analysis that he asserts demonstrates that law and chance working together cannot generate CSI, either. Dembski and other proponents of ID contend that CSI is best explained as being due to an intelligent cause and is therefore a reliable indicator of design.