The recent news of Heng Swee Kiat assuming the position of 1st Assistant Secretary-General of People's Action Party while Chan Chun Sing assuming 2nd Assistant Secretary-General has Singaporeans talking about how Heng would naturally become the next PM of Singapore.
However, going through the history of PAP, this may not necessarily be so.
In fact, among the second generation PAP leaders, Goh Chok Tong became the PM despite the fact that he was the 2nd Assistant Secretary-General of PAP after Tony Tan, who became 1st Assistant Secretary-General. This was after the PAP CEC election in 1980.
In Goh's biography, "Tall Order: The Goh Chok Tong Story", it was revealed:
Goh recalled, "LKY told me he wanted to make Tony the first assistant sec-gen, so I said okay."
"It has always been my attitude: okay, no problem. The good thing is I never aimed for the top post," he added.
Tony Tan didn't want the job
Hence, as can be seen how PAP works, the PM of the day has a lot of say to decide who would be what inside the party.
As things turned out, Tony Tan did not become the PM but Goh did. And the reason was: Tony Tan did not want the PM job. This was revealed by LKY in 1988:
Hence, coming back to Heng, it's not a done deal that he would become the next PM by virtue of the fact that he is now the 1st Assistant Secretary-General of PAP.
Using PAP history as a reference, Chan, who is the current 2nd Assistant Secretary-General may well become the PM, just like Goh did.