Gustav Bergmann, Meaning and Existence (Madison: University of Wisconsin Press, 1959, p. vii):
Philosophy is dialectical. This means, among other things, that critical examination of the positions he rejects is an important part of a philosopher's argument for the position he adopts.
I would add that philosophy is also aporetic. The positions a philosopher affirms are responses to problems and cannot be understood otherwise. The problems are logically primary; solutions in the form of theories and theses are logically secondary. As Plato puts it at Theaetetus 155, "wonder is the feeling of a philosopher, and philosophy begins in wonder." This passage is expressive of the aporetic sense.