ABSTRACT
How to Reason: A Critick of Arguments is the title of a projected treatise on logic on which Charles S. Peirce worked extensively in 1894. In "What is a Sign?" Peirce defines a sign or representation as something "which conveys to a mind an idea about a thing". Monstrative signs show the structure of composite assertions and of arguments. In both How to Reason and the Short Logic, the analysis of the elements of assertion and inference is based on a preliminary investigation of the principal modes of signifying of terms, and thus on a classification of signs. There are three principal kinds of signs: icons, indices, and symbols. Indices and symbols are necessary to express assertions; but deductive reasoning is formal reasoning in so far as it depends on forms, and the only kind of sign that can directly display a form is the icon.
