According to Napoleon Mabaquiao Jr., in the strict use of the word philosophy in the academe (strict use of philosophy), there are three fundamental hallmarks of philosophical works:
- Topic: a philosophical work asks questions about foundations
- Methodology: a philosophical work uses methods from philosophical traditions
- Arguments: a philosophical work uses argumentation to advance ideas
However, I think these three fundamental hallmarks of philosophical works are restricting.
References
Mabaquiao, N. (2011). Isang Paglilinaw sa Kahulugan at Kairalan ng Pilosopiyang Filipino = A Clarification in the Existence and Meaning of Filipino Philosophy. Malay, 23(2), 39–56.