Does the Word yom (יום) in Genesis 1 Definitely Mean a 24-hour day

This was an argument by a Reddit user. Here is a simplified version:

First he tried to steelman his opposition:

The word “day” is extremely flexible. It can mean so many things: It’s impossible to know what they mean. The word “day” could mean anything! 

Then he goes into his defense of yom = 24 hours day

Except, of course there aren’t! Every single English speaker who reads that sentence will interpret “day” in the exact same way: the 24-hour unit of time. There is absolutely zero ambiguity. Common words like “day” often have multiple meanings, but in the vast majority of sentences, it’s very clear which meaning is intended. The context puts tight constraints on which sense of the word applies.

Hebrew is my first language, and it has some quirks of its own. For example, the Hebrew word for “day” is “יום” (pronounced “yôm”), and it is has multiple meanings:

• 24-hour time span: “‏‏אחרי יום וחצי הם מצאו את הפתרון.” (“After a day and a half they found the solution.”)
• Just the 12 hours of light: “הוא עבד ביום וחגג בלילה." (“He worked during the day and partied during the night.”)
• An unspecific majority of a 24-hour timespan: ‏״לקח לה כל היום לנקות את הגינה״ (“It took her the whole day to clean the garden.”)
• A general period of time of any length: “‏בימים ההם הלכנו לבית ספר יחפים בשלג!” (“In those days† we walked to school barefoot in the snow!”)

One place where this word is used is Genesis 1. That story describes the creation of the world in six yôms. For example:

ויהי־ערב ויהי־בקר יום שליש 

And there was evening and there was morning, the third day. (Genesis 1:13)

Yes, yôm has multiple meanings, but it is very clear which meaning is intended in this sentence.

But if you don’t speak Hebrew, how do you know which sense of the word yôm applies here? In this case, we have a definitive answer immediately because of the grammar. The noun yôm has an ordinal numeral attached to it, shlishí (שלישי, meaning “third”). yôm with an ordinal numeral cannot mean a general time period. Just like in English: “back in my day” doesn’t work if you change it to “back in my third day.” If the yôm is numbered, it is a 24-hour day. Period. Literally just that single word already locks down the meaning with zero ambiguity.

However, Genesis 1 is very generous and gives us a mountain of additional confirmation through its context. This yôm does not just have an ordinal adjective, it’s a part of a set of six yôms; that also forces it to be a 24-hour day. The yôm explicitly has an evening and morning – which the generic time period sense of yôm does not. The yôms are associated with the cycle of light and darkness, which again ties them directly to the actual 24-hour daily cycle, not to some longer epoch. To be clear, we do not need more context; each of these individually would completely rule out a reading of yôm as something other than a 24-hour day. But it is very nice of the author to make it double-triple-quadruple obvious that these are 24-hour days. In fact, it’s rare for any sentence to be this overly explicit about which meaning of yôm it’s using, going out of its way to delineate it using evenings and mornings. If there was a divine author behind this text, they tried very hard to make sure people wouldn’t misinterpret yôm. (Not that it helped.)

Definitional fallacies like this, where someone with no knowledge of Hebrew wields a lexicon like a hammer and beats a verse into whatever shape they please, are becoming more common as free lexicons become more accessible. But lexicons are not a choose-your-own-adventure book and Hebrew is not some silly-putty language where everything is malleable. If you want to read this story allegorically and say each day is a metaphor for a longer age, fine; I have a separate post in the works refuting that. But don’t pretend it’s what the Hebrew says, because it obviously isn’t. It’s just like the English example from before – you instantly knew that the sentence “On the third day Bob was at the office from sunrise till sunset” didn’t refer to some unknown long period of time. You didn’t need to do any grammatical analysis. It was clear as day.

My Rebuttal

Based on a linguistic and theological evaluation, the statement "The word יום (yôm) in Genesis 1 definitely means a 24-hour day" is contested. While it represents the standard literalist interpretation, the qualifier "definitely" is debated by scholars, theologians, and even ancient church fathers who argue the text allows for, or requires, nuance.

Here is an evaluation of the evidence for and against that statement:

Arguments Supporting the Statement (Why it might mean a 24-hour day)

Proponents of the literal view argue that the Hebrew grammar is unambiguous and follows a specific pattern used elsewhere in the Bible to denote solar days.

• Ordinal Numbers: In the Old Testament, when the word yôm is modified by a number (e.g., "first day," "second day"), it almost exclusively refers to a standard 24-hour period.

• "Evening and Morning": The refrain "and there was evening and there was morning" (Gen 1:5, 8, etc.) defines the boundaries of the days. Literalists argue this phrase loses meaning if the "day" is an epoch of millions of years.

• The Sabbath Pattern: In Exodus 20:11, the command to rest on the Sabbath is grounded in the creation week ("For in six days the Lord made the heavens and the earth... and rested on the seventh"). The argument is that for the analogy to work (humans work 6 days, rest 1), the original creation days must be the same type of days humans experience.

Arguments Challenging the Statement (Why it might NOT be a 24-hour day)

Critics of the "definitely" claim argue that the internal logic of the text and the immediate context suggest these days are not standard solar cycles.

• The "Day 4" Problem: The sun and moon—the celestial bodies that define a 24-hour solar day—are not created until the fourth day (Gen 1:14-19). This leads many people, laypersons and scholars, ancient and modern, to ask how the first three days could be 24-hour solar days without the sun.

• Immediate Context (Genesis 2:4): Just a few verses later, the text uses the singular yôm to refer to the entire creation week combined: "These are the generations... in the day [yôm] that the Lord God made the earth and the heavens." Here, yôm clearly means an era or period, not 24 hours.

• The Seventh Day: Unlike the first six days, the seventh day (Gen 2:2-3) does not close with "and there was evening and there was morning." Many theologians interpret this as an eternal day of God's rest that is still ongoing (referenced in Hebrews 4), suggesting the "days" are divine epochs rather than human clock-time.

• Historical Precedent: The idea that yom means 24 hours was not the universal view before modern science. St. Augustine (4th century), for example, argued that the days were not solar days but God's instantaneous work explained in a literary framework for human understanding. This is, of course, not definitive proof of the "days = epoch" view, just proof that the literal 24 hour day has been questioned for centuries.

Conclusion

From a strictly lexicographical standpoint, yôm is the standard Hebrew word for "day." However, because the text itself applies this word to 1) a period before the sun existed (Days 1-3).  And 2) uses it largely for a divine week; the claim that it "definitely" refers to a 1440-minute period is an interpretative choice, not an indisputable linguistic fact.

Verdict: The statement "The Word yom (יום) in Genesis 1 definitely means a 24-hour day" is a specific interpretive conclusion, not a settled linguistic fact. The text allows for a 24-hour reading, but the internal context (especially Day 4) provides strong grounds for alternative views.