For some reason, there appears to be confusion – still (even among some Apple press) – about why this year’s phone is not called the iPhone 6, and is instead called the iPhone 5s. Outside of the original year, a very predictable pattern exists – so far.

In even-numbered years, a completely new phone arrives, with a redesigned chassis. In odd-numbered years, a revised “S” (now “s”) phone arrives, which carries over most of the chassis of the previous year, but generally focuses on internals and additional hardware improvements.

Following the original iPhone in 2007 (a unique chassis unto its single iteration), the pattern so far has been:

1. 2008 – 3G
2. 2009 – 3GS
3. 2010 – 4
4. 2011 – 4S
5. 2012 – 5
6. 2013 – 5s (and renewal/rebody of 5 as 5c)

So next year, if the pattern holds, we’ll see an iPhone 6, with a pretty significantly redesigned body (while the 5c likely moves down to the subsidized free slot and a 5s – possibly enrobed in polycarbonate – moves down to the subsidized $99 slot).