Floyd Parker, «The Terms "Angel" and "Spirit" in Acts 23,8», Vol. 84 (2003) 344-365
In any discussion of the Sadducees, there will always remain a certain amount of doubt due to the paucity of sources about them. Based on what data has survived, the older theory that the Sadducees rejected the extravagant beliefs about angels and spirits provides the most convincing solution to the problem of Acts 23,8. The Sadducees’ reasons for rejecting these views were twofold: 1) angels were integrated into the apocalyptic world view that they rejected; and 2) angels often served as God’s servants to administer predestination or providence. Thus, when Paul claimed that a heavenly being had appeared to him in a manner and with a message that appeared to be predestinarian in nature, the Sadducees were unwilling to entertain the idea that an angel or spirit had appeared to him. Certainly new theories will arise in an attempt to grapple with this issue, but to re-appropriate the words of Jesus in Luke 5,39, "the old is good enough".
Daube also employed Peter’s angel (Acts 12,15) as further proof for an angelic interim. In this passage, Peter had just been delivered from prison and stood knocking at the gate of a house where a group of Christians was praying for him. When a servant girl, in her excitement, left him outside and informed those praying inside that he was at the gate, they told her that it was his angel (o( a!ggelo/j e)stin au)tou=). Some commentators believe this is evidence of the belief in a special type of guardian angel "who is the exact image of his protégé"32. Daube proposed instead that these Christians understood this to be Peter in his angelic, interim state. His reason for rejecting the guardian angel interpretation was because the rabbinic evidence for this notion is "thin". He is correct that this particular type of guardian angel (i.e., a celestial double) is not well attested. Be that as it may, the biblical and extra-biblical evidence is thick with the notion of guardian angels (Gen 48,16; Dan 3,28; 6,22; Matt 18,10; Heb 1,14; Tob 5,22; LAB 15,5; 59,4; Test. Jacob 1,10). Perhaps this was Peter’s guardian angel or perhaps this figure was designated "his angel" simply because it had delivered him from prison before (the same a!ggeloj kuri/ou; Acts 5,19, 12,7). Whatever the correct interpretation is, in the absence of more compelling evidence, this example cannot serve as proof for an angelic interim state.
Probably the most compelling reasons for rejecting the identification of "angel" and "spirit" is that Luke himself does so. His use of "neither ... nor" (mh/te a!ggelon mh/te pneu=ma; Acts 23,8) and "or" (pneu=ma ... h@ a!ggeloj; 23,9) distinguishes between "angel" and "spirit" and thereby indicates they are not regarded by him as synonyms33.
In summary, Daube’s theory is untenable because he: 1) failed to locate texts that specifically used "angel" and "spirit" as synonyms for disembodied humans during the interim period34; 2) failed to demonstrate that being "like" an angel was the same as becoming an angel; and 3) the author of Acts indicates by his language that these words are not synonyms. Therefore, it seems unlikely that the Sadducees were being portrayed as rejecting the belief in the intermediate state in Acts 23,8, even though that was one of the beliefs they did deny elsewhere (e.g., BJ 2.165).