Step 1: Understanding the methods of philosophical debate.
In Indian philosophy, debates or discussions are structured around several methods:
- Vada: A method of debate that seeks to uncover the truth through dialogue and reasoning, without any intention of defeating the other.
- Jalpa: A method of debate that focuses on defeating the opponent through argumentation, typically by exposing their flaws.
- Vitanda: This is a method used to refute an opponent's arguments without necessarily offering a constructive alternative.
- Samsaya: This refers to doubt or skepticism, but it is not considered a structured method in philosophical debates.
Step 2: Conclusion.
The correct answer is 4. Samsaya, as it refers to doubt rather than a method of philosophical engagement.
Final Answer:
\[
\boxed{\text{The correct answer is 4. Samsaya.}}
\]