Okay, so I am posting this because a number of friends have been asking me about the differences and similarities between a special Parliamentary Select Committee and a Commission of Inquiry in the Singapore system. This is my effort to simplify and clarify matters. Please do let me know if there are any mistakes. I certainly do not have the last word.
In essence, both a special Parliamentary Select Committee and Commission of Inquiry can be tasked with establishing the facts of matters referred to them. These two bodies are most appropriate for dealing with issues of government policy or extending oversight. Functionally, they can be quite similar. Where they differ are in composition and where they draw their authority–Parliament in the case of the former and the President in the case of the latter.
There are also some differences in procedure. One perhaps salient procedural difference is that when deciding on issues in a select committee, members get to vote and can call for a division that records each vote in accordance with Section 104 of the Parliamentary Standing Orders. That may give room for a dissenting opinion the official report it submits to Parliament in a way that a COI is not bound to. Something similar may be possible under a COI, but the President must explicitly lay it out in accordance with Section 3 of the Inquiries Act.
Parliamentary Select Committees and Commissions of Inquiry generally do not establish legal liability. They also do not deal with personal matters, including legal disputes. Those responsibilities lie with the judiciary (i.e. the courts). That means to say that the existence of hearings by special Parliamentary Select Committees and Commissions of Inquiry are not an indication of wrongdoing.
The legislature (Parliament) convenes a Parliamentary Select Committee and the President issues a Commission of Inquiry. The executive in the shape of the cabinet and civil service, legislature, and judiciary are different branches of government. This distinction is to allow for the separation of powers to ensure that no branch is able to abuse authority. In Singapore, the legislative branch also includes the Presidency, which is supposed to be an additional check on the executive powers of the cabinet.
For relevant details on specially appointed Parliamentary Select Committees, please consult the Standing Orders Sections 103-106: https://www.parliament.gov.sg/sites/default/files/Standing_Orders_of_the_Parliament_of_Singapore_(Online_Version%202017).pdf
Sections 12-17 and 31 of the Parliament (Privileges, Powers, and Immunities) Act (Chapter 217) provides a further indication of the powers of a Select Committee working on the authority of Parliament:
On Commissions of Inquiry, please refer to the Inquires Act (Chapter 139A), particularly Sections 3, 4, and 15: http://statutes.agc.gov.sg/aol/search/display/view.w3p;ident=e33c6a9c-6b49-43a7-b3f8-f7cb70b3e579;page=0;query=DocId%3A%22f35daedd-b4da-4944-9bf4-457e1fc931d0%22%20Status%3Ainforce%20Depth%3A0;rec=0#P1II-.