In the vast majority of cases - over 100 suttas, the first jhana is described as having only the 4 factors listed above. However the Abhidhamma and the Commentaries do speak of 5 factors for the first jhana - they add ekaggata (one-pointedness). Ekaggata isn't mentioned in the suttas because it is not and cannot be part of the formula. In the first place, vitakka and vicara always and only mean "thinking" and "examining" in the suttas - there is no place where they can be interpreted to mean "initial and sustained attention" or any such thing. It is even explicit in the canon that vitakka and vicara refer to thinking in the context of the first jhana - see for example SN 21:1. There "Noble Silence" is defined as the 2nd Jhana because vitakka and vicara are now absent. It is simply not possible to have one-pointedness and thinking at the same time, so experiencingekaggata in the same jhana as vitakka and vicara makes no sense whatsoever.
Furthermore in the 2nd Jhana, vitakka and vicara are replaced with "vupasama, ajjhattam sampasadanam" and "ekodi-bhavam" - "inner tranquility" and "unification of mind." If there wasekaggata in 1st Jhana, there would be no need to specify the gaining of "ekodi-bhavam" to replacevitakka and vicara in the 2nd Jhana.
Now there are 2 suttas where 5 factors are given for the first jhana and a 3rd sutta where unification of mind is mentioned in regard to the 1st Jhana:
- M I 294 - MN 43 "The Greater Set of Questions-and-Answers"
- M III 25-29 - MN 111 "One After Another"
- S IV 263 - SN 40.1 "The First Jhana" (not ekaggata, but ekodim; the context makes it a real stretch to consider this a 5th factor!)
Of course this was a problem for the abhidhammaikas and the commentators. So they redefinedvitakka and vicara to mean initial and sustained attention. But clearly the Abhidhamma has tinkered with the definitions of the jhanas, converting the first jhana into 2 different states: one withvitakka & vicara and one with only vicara. There is no basis for this in the suttas except again in a couple of "late" suttas.
And by the time of the Visuddhimagga, the definitions of what constitutes a jhana had diverged significantly from the sutta definitions. The Visuddhimagga has made the jhanas so difficult that only one in a million who come to meditation can enter the first jhana (section XII.8) - while in the suttas, the monks and nuns were all practicing jhana (the Buddha didn't have millions of followers - probably only a few thousand at most, yet there are many accounts of monastics successfully practicing the jhanas). The absorption level described in the Visuddhimagga is so deep that "sounds are a thorn to the 1st jhana" as found in AN 10.72 makes no sense at all.
Clearly ekaggata as a factor of the 1st jhana is a later addition making the 5 factors of the 1st jhana a later schema. In fact, looking at the jhanas with the traditional abhidhamma/commentarial factors misses some of the important information in the sutta schema - see http://leighb.com/jhanatrd.htm
Source:
http://www.leighb.com/jhana_4factors.htm