I was toying with the idea of doing one of my "how the voting system works" blogposts just before the SNP leadership ballot got underway, but I began to think it was unnecessary because I had looked back at past internal elections in different parties and realised that the vast majority of members do actually rank more than one candidate. However, our regular commenter Keaton has gone and put a doubt in my mind by saying that he thinks Humza Yousaf might sneak the win, because not enough Ash Regan supporters understand the voting system and therefore may not give any second preference at all. I'm not at all sure that's true, but just on a belt-and-braces basis, here's a reminder of why using a second preference is so vitally important and why it's a totally risk-free thing to do.
The name of the voting system being used in the leadership ballot is the Single Transferable Vote, and it's the same system used in multi-member local election wards in Scotland - although in practice when only one person is being elected it is functionally identical to the Alternative Vote system that the UK had a referendum on back in 2011. The name Single Transferable Vote helpfully sums up the system in quite a literal way. It may seem strange to call it a 'single vote' when you're able to rank more than one candidate, but it genuinely is 'single' in the sense that it can only be in one place at any one time - ie. on any given count, it will only count towards one candidate's tally of votes. There will be no 'half-votes' or 'diluted votes', so you don't need to worry that your first preference vote for Ash Regan will somehow be 'less emphatic' if you give a second preference to Kate Forbes. (My guess is that's the irrational worry that causes some people to wrongly use only their first preference vote.) When the first preference count is revealed, everybody who gave Ash Regan their first preference will simply have cast one vote for Ash Regan and for nobody else. There will be no distinction made between Regan voters who gave a second preference and Regan voters who didn't. Those will all just be Regan votes and nothing else.
However, if Ash Regan is eliminated after the first count (as we strongly suspect she will be), you then actively want your single vote to be transferred to another candidate for the second and final count. You can't do Regan any good whatsoever by not having your vote transferred, because in the second count she's not a candidate anymore. Your first preference for Regan has already been recorded and will be reported in the media, so there literally is nothing to be gained by not giving a second preference - which would be tantamount to abstaining on what will be a Yousaf v Forbes run-off on the second count. If you prefer Forbes to Yousaf (as most Regan supporters do), not giving a second preference means you are passively helping Yousaf to beat Forbes, which is an utterly perverse thing to do - and let's be honest, Ash Regan herself would not thank you for doing that. I have no doubt that she'd far rather serve in a senior Cabinet post under First Minister Kate Forbes than find herself languishing on the backbenches under "First Activist" (ahem) Humza Yousaf.