His second work, published in 1898, was a book on formal logic.

This book provides a course in the construction of the real numbers based on formal logic.

At this point an opponent of formal logic, he changed position and wrote a text book on it.

But with humans you get language, consciousness, and fully developed formal logic.

The expressions are statements in formal logic which can be true or false.

In the early decades of the 20th century, the main areas of study were set theory and formal logic.

This statement in formal logic would not allow the prisoner's argument to be carried out.

Later, with the rise of formal logic a logical truth was considered to be a statement which is true under all possible interpretations.

The problem is how a formal logic of nonmonotonic reasoning should deal with such cases.

Russell, in particular, saw formal logic and science as the principal tools of the philosopher.