Invalid conclusions are usually of one type based on the insufficiency of the premises, data or considerations. Fallacious logic, however, can be exhibited by over 18 different types, and in the logic of the all-important syllogism, where there are 256 possible forms of the categorical variety alone, the possibilities for inherently fallacious structures are numerous.
Assertions that conclusions may be drawn or derived from insufficient premises and consideration are examples of a popular defect in reasoning. It is probably the greatest and most pernicious habit of homo 'sapiens', and it has governed the life, organization and politics of many societies from ancient times. The lessons of the physical sciences, of experimental method and of scientific methodology in the last three hundred years show what correct argumentation can accomplish – that is, the establishment of conclusions from true and adequate premises. The power of cogent reasoning unfortunately has not penetrated as well in the social and behavioural sciences. Paradoxically, the study of logic was eliminated from higher education as the particular sciences were incorporated into it.
Parallel to the development of interdisciplinary sciences and generalized and more holistic curricula, logic is re-emerging – particularly in mathematics, linguistics and information theory as applied to computer and robot developments. Artificial intelligence may yield the perfect reasoning that has eluded human intelligence.
Logic can never decide what is possible or impossible.