Chapter 2 surveyed all of Euler’s publications, manuscripts, notebook records, and correspondence relevant for the development of PAM. Then Chap. 3 paraphrased Euler’s notebook records related to this development. Appendices A, B, and C contain full-length transcriptions and translations of these documents. On that textual basis, we are now in a position to analyze and reconstruct the development of PAM within Euler’s scientific framework and “program” for mechanics based on these writings. They may be incomplete, yet they count as the fundamental historical facts for the purposes of interpreting this development, chronologically and in regard to content: by connecting them according to causal and/or plausible reasons. Historiographically, this approach seems to be most transparent and comprehensible. However, the conclusions and results depend on the selection of these documents considered from all available sources associated with Euler’s monumental scientific heritage. More precisely, from the part we may regard as “relevant” for our purpose. Moreover, this selection depends on concepts and formulas introduced and used by Euler that we considered essential and relevant for the development of PAM. By selecting and connecting them so as to reconstruct Euler’s line of thoughts, we inevitably bias the resulting reconstruction. This is, however, hard to avoid and is inherent in all interpretation. But if this kind of interpretation happens in a causal, reasonable, and intelligible way, the result will map the historical truth as close as possible. Since we provide all original documents parallel to this reconstruction, it should become as transparent and comprehensible as possible.