Necessary or immediate knowledge (ʿilm daruri) is acquired without a deliberate process of inference; the certainty generated by a properly established mutawatir report is an example in this discussion. Inferential knowledge (ʿilm nazari) arises through investigation, comparison, reasons, and assessment of corroborating circumstances.
For example, an expert studies the routes of a report, the accuracy of its transmitters, agreement among its channels, and possible hidden defects. From the combined evidence the expert may reach a conclusion regarded as certain. That is a product of investigation, not of merely hearing a statement.
Maintaining this distinction avoids treating tawatur and particular corroborated ahad reports as producing knowledge by precisely the same route.