What is the meaning of the terms "consciousness' and "to be conscious of something"? What does it mean, when we say that humans are conscious, but animals perhaps are not? The answer suggested in this paper is simple, but in order to substantiate it, some preliminary deliberations cannot be avoided. There is, of course, some vagueness in the current use of the term "consciousness' and there are practically no definitions or explanations of that term to be found in the present "philosophy of mind", yet the case is not a hopeless one. In order to analyze what is or could be meant by "consciousness' one first has to find a set of statements concerning or containing this term, which are commonly accepted. (Should this set be empty, any discussion on consciousness would be unintelligible). I call this set the "canonic phraseology" of the terms "consciousness' and "to be conscious of". This phraseology can be derived especially from philosophical texts of the 17th and 18th centuries, which may seem antiquated in the age of mass produced papers on "the phenomenon of the mind in the computer age", but there is a good reason for looking back.