We decipher the Earth's diary that has been left us as a legacy. We read with trained senses and interpret with the tools of disciplined thinking. We translate the Earth's language into our own, and enrich the already bright and colourful surface of the present with the knowledge of the inexhaustible abundance of the past. Hans Cloos, 1953.
Almost alone among modern sciences, geology has preserved a method of inquiry that emphasizes synthetic reasoning for the interpretation of Earth's signified causal processes. Though geologists interpret Earth's signs via all manner of measurement, quantitative modeling, and experimentation, these are but tools for an inquiry ultimately directed at the truth of Earth's message. Geologists have always considered that message to be signified in rocks, sediments, fossils, and other signs of Earth processes. To interpret these signs, geologists do not need a foundational metaphysics to ground their reasoning, as Lyell attempted with his uniformitarianism. Instead, geologists can benefit from understanding the formal conditions of what will count as true in these signs, a topic explored through the branch of philosophy known as semiotics. The geologically relevant philosophy involves a semiotic point of view wherein signs are not mere objects of thought or language, but rather are vital entities comprising a web of signification that is continuous from outcrops to reasoning about outcrops. Such an action of signs constitutes a geosemiosis that leads geological investigators on a fruitful course of hypothesis generation. Semiotic grammar provides the means to describe the representational character of signification that is inherent in this geological reasoning. Critical logic explores the modes of inference used to seek truth in the representations, and georhetoric attains truth as a matter of belief. While not being a method for doing geology, semiotics provides a means of describing the highly productive reasoning processes of geologists.