Why can’t I use a lemon instead of an etrog?

Question:

How do we know that we must take an etrog as the fruit in the Four Kinds, and that I cannot just use a lemon or an orange?

Answer:

The Torah1 describes the fruit which we must take as פרי עץ הדר—pri etz hadar, which translates loosely as the “fruit of a tree which is hadar.” What is hadar?

Since the days of Moses, we have known this to be an etrog. There was never a time when the identity of the fruit needed was in doubt. Rather, each generation told the next generation which fruit was needed to complete the Four Kinds.2 Nevertheless, various propositions were made to demonstrate that this can also be understood from the text.

The common meaning of הדר hadar is “beautiful.” Ibn Ezra3 writes that the etrog is known as the most beautiful of all fruits, and when the Torah tells us to take a beautiful fruit, the only possible candidate is the etrog.

Alternatively, Nachmanides4 writes that hadar is actually the ancient Hebrew name for the etrog, the latter being its Aramaic name. Hence the verse is simply telling us to take the fruit of the etrog tree.

The sages of the Talmud,5 knowing that this term referred to the etrog, found a number of creative ways of seeing the etrog’s distinct properties in the above-mentioned verse:

1. Focusing on the first two words of the description, “fruit of a tree,” the Talmud understands this to refer to a tree which tastes similar to to its fruit. The wood of the etrog tree is similar in taste to its fruit.
2. Rabbi Judah the Prince points out that the word הדר hadar can also be rendered as הדיר hadir—a sheep pen. Just as a pen has both old and young animals, so does the tree in question have old and young fruit at the same time. This refers to the etrog tree, whose fruit continues to grow through all seasons, allowing for a single etrog tree to simultaneously hold fruits in multiple stages of growth.
3. Rabbi Abahu suggests that hadar can also mean “the resident.” This means that this is the fruit which is a resident on its tree—referring to the etrog’s prodigally long growth period.
4. Ben Azzai said that hadar is etymologically related to the Greek hydor (water)—from which the English word “hydration” is derived. This is a reference to the fact that the etrog tree needs a lot more water than other trees.

As I wrote, all of these suggestions are purely academic, since we have known since the Giving of the Torah that the fruit which we needed to take is the etrog.

Please let me know if this helps.

Yours truly,
Rabbi Menachem Posner