Sotah 067

4:
So the sages must now show how it can be that even though the case of lesser severity (the 'earlier testimony' of the injunction against consorting with a certain party) requires two competent witnesses, the case of greater severity (the 'later testimony' of infidelity) nevertheless can be substantiated with less competent witnesses.

5:
The 'earlier testimony' creates a situation in which a woman becomes forbidden to her husband temporarily: if she survives the test of the 'cursing waters' her innocence must be presumed and conjugal relations resumed. Now the Torah [Numbers 5:13] states that the ceremony of the 'cursing waters' takes place in circumstances in which there is no testimony whatsoever available as to the woman's infidelity:

The phrase 'and she wasn't raped' tells the sages that what the Torah is referring to here is, in fact, not the 'earlier testimony' but the 'later testimony': the woman was 'defiled' (was unfaithful); and this testimony of infidelity may be substantiated even in a situation in which "there is no witness against her" that she was untrue to her husband. How can there be testimony when there is 'no witness' to testify? The answer to this conundrum, say the sages, must be that the words 'no witness' mean that there is no testimony of the quality that would be considered acceptable in other cases.

6:
The presumption of the sages is that wherever in the Torah testimony is required that testimony must be offered by a minimum of two witnesses. The main reason for this requirement was described by us when we studied Tractate Sanhedrin:

The Torah [Deuteronomy 19:16-19] stipulates a very simple rule:

In order to prove that witnesses are not conspiratorial it must be possible to compare their evidence. That is why the Torah [Deuteronomy 19:15] states quite clearly:

7:
Our mishnah now introduces a rather problematic manner of logical inference. The technical term for this method is 'Gezerah Shavvah'. To our modern sensibilities this particular form of inductive reasoning can seem very tenuous – and, indeed, the sages would only permit the use of a Gezerah Shavvah when it had been handed down from time out of memory. It basically involves finding a word that occurs in two different contexts, where its use in the one context illumines its use in another. In our present case the word in question is 'davar'. In Hebrew this word can bear many meanings: thing, something, word etc. In the above quotation from Deuteronomy it bears the meaning of 'a fact'. Now this word occurs in the Torah in hundreds of contexts with hundreds of possible connotations, but only one other context is of interest to the sages in this particular matter:

The Torah [Deuteronomy 24:1-4] states:

The sages were later to ask whether the right of the husband to dismiss his wife was curtailed in any way by implication in the Torah. Two major views emerged from this discussion. Both were centered on the words of the Torah which I translated above as "something wrong". The Hebrew, Ervat Davar, can be understood in two ways. It can be understood to indicate that the husband finds 'something' wrong with his wife – that is to say 'anything': the marriage just fails for any reason. The alternative understanding is connected with the word Ervah, which almost always in Scripture bears a sexual connotation. This second interpretation would indicate that a man divorces his wife because he has found in her some immorality.

In any case, the word 'davar' is here associated with infidelity and in the previous quotation the same word is associated with the need for a minimum of two witnesses.

8:
Now the Torah has specifically permitted the testimony of only one witness for the 'later testimony' therefore it must be clear (to the sages at least!) that the requirement for two witnesses in the case of the Sotah must apply to the 'earlier testimony'.