What is the meaning of "the 'illah (effective cause) that is of the nature of warning (tanbīh) and intimation (īmāʾ)" according to Al-Amidī, and what is the difference between "waḍʿan" (by وضع - placement/setting) and "bi-waḍʿihi" (by its وضع - placement/setting) in the context of his statement: "The third method is that which indicates causality by warning and intimation, and that is by the 'illah (effective cause) being necessarily derived from the linguistic meaning (madlūl al-lafẓ) by وضع (placement/setting), not that the word indicates causality by its وضع (placement/setting)"? Is it understood from his words that this 'illah is of the nature of the Arabic language?

The definition of īmāʾ (hinting) and tanbīh (alerting) is clear. Al-Amidī's intent is that the indication of īmāʾ is achieved through implication (iltizām), not through the explicit meaning of the wording. Thus, the method of īmāʾ understands causality from the meaning, not the wording. Al-Zarkashī clarifies that īmāʾ and tanbīh indicate causality by implication, because mentioning them alongside a ruling prevents them from being without benefit, so the apparent conclusion is that they are the cause. Al-Shanqītī further clarifies that the indication of īmāʾ and tanbīh specifically pertains to the cause of a ruling. Its criterion is that a characteristic is mentioned alongside a ruling in such a way that if the characteristic were not the cause, the speech would be flawed. An example is the Prophet's (peace be upon him) statement to the Bedouin: "I am ruined; I had intercourse with my wife during the day in Ramadan (definition). Emancipate a slave." If the intercourse were not the cause for emancipation, the speech would be flawed. All of this falls under the indication of implication (dalālat al-iltizām). This is a technical Usuli (principles of Islamic jurisprudence) definition, and īmāʾ and tanbīh have examples and types that further clarify the definition.