Aristotle started this particular chapter of the Topics, Book 1 by saying that he would say what deduction is and what the various kinds of deduction are. The last argument claimed that even specialized arguments were not exceptions to his division. Aristotle continues,
The foregoing must stand for an outline survey of the species of deduction. In general, in regard both to all that we have already discussed and to those which we shall discuss later, we may remark that that amount of distinction between them may serve, because it is not our purpose to give a precise definition of any of them- we merely want to describe them in outline: we consider it quite enough from the point of view of the line of inquiry before us to be able to recognize each of them in some sort of way.
What Aristotle previously argued for is only enough to distinguish between the various forms of deduction. We do not need to be more precise than that because we should focus on the objective of this particular book. This book only requires that we recognize dialectic deduction since that is what it discusses.
Aristotle has correctly described his position. There is no obvious reason why deduction cannot be divided the way that he suggests. He does not need an argument for the division. He only needs enough to recognize the division and for the division to be true. Arguments that a proper categorization of deduction is dialectic deduction and demonstrative deduction will have to come from somewhere else.
Having completed this task, we must continue on to the reasons for studying dialectic.