—namely, the analogy (1) along with the “consensus” they allege—actually substantiates this very claim (2).
The general foundations of the people of innovation and vain desires—those who depart from the Book and the Sunnah—are typically built on just that: a particular kind (3) of analogy they themselves devise, a model they advance to oppose what the messengers brought, and a sort of consensus they merely assert. From that rational analogy and this purported transmitted consensus they construct the core of their religion.
Hence you will find Abū al-Maʿālī—who is the shrewdest (4) of the later scholars—relying, in what he touts as decisive proofs, on precisely such methods.
Likewise, the leading dialecticians driven by their own whims, such as Abū al-Ḥusayn al-Baṣrī (5), his teachers (6), and those of their ilk, in many instances rely neither on the Book, nor on the Sunnah, nor on any accepted consensus. Rather, they separate themselves from the Community, whose consensus is well-known, by means of the composite consensus they themselves claim; just as they contradict the clear dictates of reason with what they call reason (7); and just as they oppose the Book and the Sunnah—the very foundations of the religion—through the doctrinal principles they invent.