Switching to a more academic mode, he propounds a speculative theory about the history of religion as proceeding through a sequence of evolutionary stages.

He was a proponent of vitalism, a popular 19th century speculative theory that claimed that a regulative force existed within living matter in order to maintain functionality.

Researchers will take blood or other bodily tissue samples for their own use in order to further their own speculative theories of human history.

To explain the existence of gamma-ray bursts, many speculative theories were advanced, most of which posited nearby galactic sources.

Meanwhile, during this time of increased media publicity of the controversy, public health officials and institutions did little to rebut the concerns and speculative theories being offered.