For practical reasons, in logic, written sentences are studied rather than thoughts in people's minds, but we should not forget that written sentences are of interest in logic only in so far as they express some thought. Semantics is about the relation between thoughts, propositions, sentences and the like, on the one hand and their object on the other hand. In a large part of this on-line logic book semantical questions will be treated. Truth is possibly the most important of the semantical concepts we will discuss, but we will say something about concepts like reference, intension and extension as well. Before this and also later on, we will also discuss other kinds of questions, first ontological questions, and then later on some syntactical ones.
All people are able to think logically correct, at least to some extent.
Consequently one doesn't need to study logic in order to be able to think logically. On the other hand, one can in various ways train one's mind, or capacity for logical thought, in order to make fewer such mistakes. One such way is the study of the science of logic. One way of defining this subject is to say that logic is a systematic study of what makes logical thought processes logical or logically correct. Within the science of psychology, on the other hand, all kinds of thought-processes are studied.