Aristotle has just finished discussing the various kinds of propositions or problems that there are. Now he will describe the difference between propositions and problems. This is from Topics, Book 1.
What we have said, then, makes it clear that according to our present division, the elements turn out to be four, all told, namely either property or definition or genus or accident. Do not let any one suppose us to mean that each of these enunciated by itself constitutes a proposition or problem, but only that it is from these that both problems and propositions are formed. The difference between a problem and a proposition is a difference in the turn of the phrase. For if it be put in this way, Is two-footed terrestrial animal the definition of man? or Is animal the genus of man? the result is a proposition- but if thus, Is two-footed terrestrial animal the definition of man or not and Is animal the genus of man or not? the result is a problem. Similarly too in other cases. Naturally, then, problems and propositions are equal in number- for out of every proposition you will make a problem if you change the turn of phrase.
We now know that there are four categories of propositions or problems: property, definition, genus and accident. It is from these categories that we get propositions and problems. All propositions and problems have the form of a question. Propositions are questions that can be answered by either yes or no. For example, Is animal the genus of man?. A problem takes a particular question and includes both yes and no answers in the question. For example, Is animal the genus of man or not? This means that there are just as many problems as there are propositions because you can turn any proposition into a problem by adding or not to a proposition.
It should be noted that Aristotles use of the word proposition and problem is not the same as our modern definitions of those words. In modern terms, proposition simply refers to the idea behind a sentence. So Jai parle Anglais and I speak English express the same proposition because they mean the same thing. A problem just refers to an problem with our reasoning. For example, we believe two things that are not consistent. These issues are the reason why all references to proposition and problem within the Topics will agree with Aristotles definition of these terms.
Next, Aristotle will explain the four categories he has established here. First, he will begin with definition.