In one of Isaiah’s prophecies (that happens to be read as the Haftarah for Parshat Lech Lecha), he describes G-d as:
“The Giver of strength to the tired (yaef), and to those without energy, an abundance of might” (Isa. 40:29).
The first part of this verse is paraphrased in a blessing recited every morning, “baruch… ha’noten la’yaef koach”. It is also commonly appended to the end of different works of Torah literature as the author’s way of expressing that his ability to endure weariness while authoring his work is from Above. However, there are another two words in the Bible which mean “tired”: ayef and yagea. In fact, the Modern Hebrew word for “tired” is not yaef, but ayef (which actually appears in the Bible a few more times than yaef does). So what, if anything, is the difference between the words yaef and ayef and how do they differ from yagea?
Some explain that yaef and ayef are actually synonymous and are indicative of a linguistic phenomenon known as metathesis (that is, the transposition of sounds or letters in a word). Thus, ayef and yaef are really the same word, but the first two letters switch positions (i.e. ayef is spelled AYIN-YUD-FEH and yaef is spelled YUD-AYIN-FEH). Indeed, Rabbi Yishaya of Trani (1180-1250), an important Italian Talmudist known as the Rid, compares the case of ayef/yaef to another well-known case of metathetical synonyms: kesev/keves which both mean “lamb” in the Bible.
Rabbi Shimon Schwab (1908-1995), on the other hand, takes a different approach. When discussing the morning blessing that refers to G-d giving strength to the tired, Rabbi Schwab focuses on the word choice of using yaef for that blessing instead of ayef. On the surface, the phraseology of the blessing simply mimics Isaiah’s above-mentioned vision, however Rabbi Schwab understands that there is more to this. He explains that while ayef and yaef both mean “tired,” they denote two different degrees of tiredness: ayef denotes somebody who is tired but still retains some energy, while yaef is somebody who is so tired that he has exhausted all his energy. For this reason, when praising G-d as the Giver of energy to the tired, we use the word yaef for maximum effect. In other words, not only does G-dstrengthen those who are tired, He also energizes those who are completely exhausted.
Rabbi Shlomo Aharon Wertheimer (1866-1935) explains that the word ayef denotes extreme fatigue to the point of fainting. Because of this, a borrowed meaning of the word ayef is “thirsty” (e.g., see Job 22:7 and Ps. 63:2) — as Radak notes in Sefer ha’Shorashim — because dehydration is generally what causes tired people to faint.
…the word ayef denotes extreme fatigue to the point of fainting….
Rabbi Yosef of Saragossa (d. 1420), a student of Rabbi Nissim of Gerona (1320-1380), explains the difference between ayef/yaef and yagea. He understands that both mean “tired” in the same way, but connote tiredness resulting from different causes. Ayef refers to one who is tired after having repeatedly performed certain movements. In this case it is the persistence of action which makes one tired. The word yagea, in contrast, refers specifically to tiredness resulting from the speed of one’s actions. In other words, one described as ayef is tired and worn out from continuous activity, while one who is yagea has depleted his energies by performing his deeds too fast and overexerting himself.
Malbim also understands that ayef and yagea refer to tiredness resulting from different causes. The word ayef refers to the regular state of tiredness which one with natural low-energy levels experiences, while the word yagea refers to tiredness which is the result of (over)exerting oneself. In fact, the very word yagea (which only appears in the Bible three times, in Deut. 25:18, II Sam. 17:2, and Ecc. 1:8) is related to the root of the verb yaga (“he toiled”).
So if you are wary of weariness and want to avoid fatigue, remember that all energy comes from G-d. As one popular figure was wont to say, “Say your prayers, eat your Wheaties, take your vitamins, and you will never go wrong”.