במדבר פרק יג, טז א לֶה שְמוֹת הָּאֲנָּשִּים אֲשֶר-שָּ לַח משֶה לָּתוּר אֶת- הֶשמ אָּרְק יַו ץֶרָּאָּה לְהוֹש עַ בִּן-נוּן יְהוֹשֻׁעַ:
We must point out that every time in the Torah and Nach that the word 'ben' appears, it has three dots (segol) under the 'beis'. However, every time it says Yehoshua's name there is only one dot (chirik), so that it is read as 'bin'. This is strange. There must be a special reason for this unusual vocalization.
There is only one other time that the word 'bin' (with a chirik) is used, and that is in Mishlei (30, 1), “These are the words of Agur, son of (bin) Yakeh...” where the 'beis' also has a chirik. [There is also another time in Parshas Ki Tetzei, Devarim 15; 2, but there it doesn't mean 'son', so perhaps that is why the author doesn't mention it.] The Sages have discussed this vocalization in the medrash, and explained it aggadically (metaphorically) in Shemos Rabba Parshas Va'era section 6. However, that explanation has no relevance to the verse here. The Sages appear to say nothing at all about our case. Nor have any of the commentaries discussed it, and this is extremely strange.
Perhaps we can explain based on the Gemara (Sanhedrin 107a) and midrashim that say that the 'yud' that was taken from the name Sarai (when it was changed to Sarah) complained about being removed from the Torah. It was only consoled when Moshe took the letter ‘yud’ and added it to Hoshea's name to make Yehoshua. In this way the 'yud' that was removed from Sarai was replaced later in the Torah.
This Gemara still leaves a difficulty. Even though Moshe ‘found the yud' to add to Hoshea's name, where did he find the vowel to go under it? The 'yud' from Sarai had no vowel under it, whereas the 'yud' of Yehoshua has a 'sheva', which is two dots. We know that the number of dots in the Torah is precise and exact, so how could Moshe add these two dots to the 'yud'? Therefore, Moshe had to remove the two dots from the 'beis' of 'ben' and replaced the 'segol' with a 'chirik'. This left two dots available which he transferred for the 'yud'.
Even though this explanation is subtle and unusual, nevertheless, because of the uniqueness of the vocalization of this word you should accept it. (This doesn't explain why he was called Hoshea 'bin' Nun before Moshe added the 'yud' (verse 8) – perhaps the 'segol' was already removed in advance of the name change?)
