Jesus resorts to a double ellipsis in John 8:58?

Let’s look at the relevant verses of John 8:

⁵⁶ Your father Abraham was overjoyed to see my day, and he saw it and was glad.” ⁵⁷ Then the Judeans replied, “You are not yet fifty years old! Have you seen Abraham?” ⁵⁸ Jesus said to them, “I tell you the solemn truth, before Abraham was, I am!” (John 8:56-58)

The critical phrase is the last one: in Greek, prin abraam genesthai egô eimi and, even more specifically, the phrase prin abraam genesthai.

Now, genesthai is the Second Aorist – Middle Deponent – Infinitive form of gi[g]nomai, which has a very broad spectrum of meanings (see Liddel-Scott-Jones Greek Lexicon), the most fundamental of which is “to become” and, only derivatively, “to be [born]” (absolute sense). Normally, in the sense of “to become”, genesthai is followed by a predicate, which is apparently not the case in John 8:58, so, the Greek phrase prin abraam genesthai is usually understood as though genesthai was actually used in the absolute sense, and consequently translated with something like “before Abraham was [born]”.

The English Unitarian Thomas Belsham (1750 – 1829), to interpret John 8:58, considered, among other arguments, that of double ellipsis (see A Calm Inquiry Into the Scripture Doctrine Concerning the Person of Christ, § 3, pp. 53-55).

The argument runs, more or less, like this. If, instead of interpreting genesthai as absolute (“to be [born]”), we suppose that genesthai means “to become” (in an elliptical sense to be determined), the key phrase at John 8:58 becomes:

[Lit. Eng.] before Abraham become [ellipsis], I am [ellipsis]

Neither “become”, nor “I am” are, reasonably, used in an absolute sense. So, there may be an ellipsis associated with each verb. Unpacking the [double ellipsis], we may have:

“Before Abraham become [father of a multitude (viz. of nations) – Gen 17:5] I am [the Messiah]”

Less obscurely, what Jesus is saying to “the Jews” may be something like this:

“And verily I say, that the time for the accomplishment of what he foresaw is not yet arrived: for before Abram shall be Abraham, i. e. become the father of many nations, according to the import of his name, I am the Christ your Messiah.” (Interpretation and paraphrase of John 8:58 provided at the Theological Repository vol. iv. p. 351, as quoted by Thomas Belsham in A Calm Inquiry Into the Scripture Doctrine Concerning the Person of Christ, p. 54)

Belsham notes that this interpretation of John 8:58 was first proposed by the Polish Socinians (presumably, the Polish Brethren, a non-trinitarian Protestant church that existed in Poland from 1565 to 1658).