It used to be called Minister without Portfolio, now it's called Minister, Prime Minister's Office. Presumably "without Portfolio" doesn't sound nice, especially in Chinese, 不管部长.
PMO Ministers are full Ministers, but don't helm a ministry personally. Usually they are Second Ministers in a ministry, so they are full cabinet positions. But because it's not nice to have their title as only Second Minister for XXX, they are given the title of "Minister, Prime Minister's Office" to remove any doubt that they are cabinet level.
For example, Grace Fu is 2M for MFA and MEWR; Iswaran is 2M for MHA and MTI.
There used to be a time in the mid 2000s when all ministers with the surname Lim are in PMO and all the PMO Ministers have the surname Lim: Lim Boon Heng, Lim Swee Say, Lim Hng Kiang, Raymond Lim, Lim Hwee Hua.
PMO Minister doesn't necessarily mean no power; the Secretary General of NTUC will always be a PMO Minister, because by custom they are cabinet positions, but they can't possibly helm another ministry, or even be Second Minister. Lim Swee Say relinquished his 2M for MND when he became NTUC Secretary General.
It is true that PMO is a "retirement" place for some; Lim Boon Heng stayed as PMO Minister for 4 years after stepping down from NTUC. Lee Yock Suan, who used to helm Labour and Education, retired as PMO Minister.
PMO Minister may also be a stop-gap measure for people who have been promoted to cabinet level, but have no "free" ministry to helm yet; case in point: Raymond Lim, who became PMO Minister in 2005, and only took over Transport when Yeo Cheow Tong retired after GE2006. The same could be said for Grace Fu and Iswaran now, though it remains to be seen if they will ever helm ministries.
Finally, PMO Minister... may be seen as "time-out" for some. It has been said that when Lim Hng Kiang didn't handle SARS properly, he was made PMO Minister for a year after being forced to step down from MOH. He has since recovered and helmed MTI ever since 2004. When LHL + 2 DPMs were both on leave in 2013, he was even Acting Prime Minister. Should be safe to say he's fully
"rehabilitated".
In any case, it is certainly puzzling that these PMO Ministers seem to always be in between jobs given that they command a high ministerial salary paid by our taxpayers money.
Tony Lee
TRS Contributor