Hang on a second, you should be asking, hasn't Paul just demonstrated that Christ has been raised in 3-7 with eye witness accounts? Why then does he need to go on extensively with this theoretical argument on whether Christ has been raised? There is a wave of conditionals, if... if... if... if... and so on. This is rendered totally useless, had he already produced eye witness reports as to the fact Christ had been raised.
Paul’s argument takes the form of a modus ponens. A modus ponens from Wikipedia ---… had their (sic) been eye witness accounts mentioned in vv3-7 there would be no need for vv12-19 at all. V.12 picks up from 1-2 with Paul's gospel, as Paul preached that Christ had been raised from the dead.
[6]” Susanne Bobzien (2002). The Development of Modus Ponens in Antiquity, Phronesis 47, No. 4, 2002.
https://en.wikipedia.org/wiki/Modus_ponens
1 Corinthians 15:12 ---
To better characterize the form of the argument, I will re-word Paul’s statement in a form that I believe has an equivalent intent, by re-wording the rhetorical question ---
Form of Paul’s argument ---
P implies Q;
P is asserted to be true,
so therefore Q must be true.
1 Corinthians 15 | The argument |
If Christ is preached that He has been raised out from the dead ...(15:12) | The P statement |
… that He was raised on the third day according to the Scriptures (15:4) … That He appeared to Cephas … the twelve … 500 brothers … James … all the apostles … me … (15:5-8) … this is what we preach, and this is what you believed. (15:11) | P is asserted to be true, |
… then you cannot deny the resurrection of the dead. [… how do some among you say that there is no resurrection of the dead? (15:12)] | so therefore Q must be true. |
One might also characterize verse 15:12, standing alone, as a tautology of sorts.
Paul follows directly with threats, he threatened the congregation with what will happen to them if they persist in their disbelief in the resurrection of the dead ---
… your faith is worthless …
… your faith is futile …you are still in your sins.
… those also who have fallen asleep in Christ [your loved ones] have perished.
… [you] are to be pitied more than all men. (15:13-19)
If 15:3-8 (or 3-11) is a late interpolation, what a ham-handed job. Certainly from a later perspective, one would expect these verses to represent post-resurrection appearances. Take the LE of Mark as an example --- the interpolator attempted a harmonization with other traditions, though shaded with his own proclivities --- it represents an obvious harmonization.
Not so with the mess in 1 Corinthians 15:3-8. Only by means of stretched apologetics can one find harmony with synoptic gospel traditions. And trying to explain the mess as an interpolation designed to settle pissing-matches between Pauline-Petrine-Jamesian or other traditions does not succeed, IMO, any better.
The key to understanding the received text is found, IMO, by forgetting all the later traditions and seeing the passage as a brief summary of the story Paul told the Corinthians during his initial evangelizing visit. It’s Paul’s back-story of the discovery of the Christ in the scriptures, and his version of how the knowledge of that scriptural discovery spread. Paul’s story claimed a wider spiritual movement in far-away Judea (as also told in Galatians) --- the perception of a wider spiritual movement that provided a foundation, traditions, needed credibility for Paul’s teachings.
The formulaic portions of the passage were composed, IMO, by one of Paul’s junior partners --- one with a proper Greek education --- likely the same one that composed the “love poem” in chapter 13, and the poetic passages at the end of chapter 15.