Q. Apart from the Haggadah, are there any other references to the four sons?A. The first thing to explain is why the Haggadah itself says that the Torah speaks of four sons.
They are not explicitly listed, but Deut. 6:20 implies a clever child; Ex. 12:26, a difficult child; Ex. 13:14, a naive child; and Ex. 13:8, a child who does not even ask.
The educational principle of the Torah is that each child needs to be handled according to his or her own capacity.
A hint of four levels of understanding is also found elsewhere in Pirkei Avot 5:18: “There are four qualities in those who sit before the sages: they are like a sponge, a funnel, a strainer and a sieve. The sponge sucks up everything, the funnel lets in at one end and out at the other, the strainer lets the wine pass out and retains the lees; the sieve lets out the bran and retains the fine flour.”
While this is not the same as the four sons, it roughly corresponds to them – the sieve is the wise son, who knows what is really important; the strainer is the wicked son who sees only the drawbacks; the sponge is the naive son, who lacks the power of discrimination; the funnel is the fourth son who does not yet retain impressions.