The Seven-Day Week


The earth's motion provides two natural divisions of time. One rotation of the polar axis defines the 24-hour day; one orbital revolution about the sun defines the year. The week is a third, intermediate time segment that is not as readily derived from observation. There is no obvious seven-day rhythm in the solar system. What then is the basis of the week? GENESIS 2:2-3 states that the weekly cycle was ordained by the Creator Himself. The very word for week, occurring 19 times in the Old Testament, comes from 'sheba', meaning "seven-period." From time to time cultures have established other arrangements of days. However, all alternatives have been temporary and the seven-day week always re-appeared in the end.

Of what interest is the length of the week to the creationist? Two particular points are emphasised in this study. First, the present calendar of weeks is a strong testimony to the pattern of the Creation activity. Liberal scholarship has attempted to turn this around, suggesting instead that the week is presupposed by the Creation narrative and is not derived from it. That is, the Genesis week is only a literary device based on man's own developed calendar - Abrahams (p.766); Van Till (p.84). This false idea needs to be refuted. Second, there appears to be a conscious effort in current literature to ignore the Biblical basis for the week. Many imaginative sources are suggested for the number seven, but Genesis is seldom mentioned. Such bias should be exposed.

Calendar Systems

Any description of historical calendars is sketchy at best. Complications and uncertainties are numerous. Parise lists more than 40 distinct calendars, many of which were altered during their lifetimes, and even this list is not comprehensive. Since there is not an exact number of earth rotations in one solar revolution, our Gregorian calendar today remains inexact. Leap year provides only a crude solution to the problem of fitting an exact number of days into the average year.

All annual calendars have needed days dropped or added (intercalation) after a period of time. Added to all this, many societies follow dual religious and civil calendars. Table I lists several representative calendars, emphasising the variable length of weeks. People have tried many ways to cluster days together in bunches of 5-10 days. Two of the recent calendars illustrate the temporary nature of any time reckoning that diverges from the seven-day week. In 1792 the French decided to institute a decimal calendar with a ten-day week. The day was further divided into decimal parts instead of hours and minutes. It failed to satisfy the people and quickly fell into disuse. The 1929 Russian entry was an attempt to dissociate time-keeping from any religious bias. Therefore, Saturday and Sunday were simply eliminated from the week! Soviet people enjoy week-ends like everyone and this calendar also was short-lived.

Abrahams (p.766) suggests evidence for an ancient Hebrew ten-day week in Scripture. He cites GENESIS 24:55 and EXODUS 12:3, however, these verses have nothing to do with the definition of the week.

Abrahams could as well have used GENESIS 7:4 and GENESIS 8:10 in favour of the seven-day week. In truth, the normal week is recognised throughout Scripture. A seven-day period is explicitly named in the days of such men as Joseph (GENESIS 50:10), Moses (NUMBERS 19:11), and Samson (JUDGES 14:12).


It is understandable that the original seven-day week was abandoned by many countries. After all, God's commands and promises were likewise neglected in the sad history of mankind. However, why has the Genesis heritage of the calendar been forgotten today? Several contemporary comments on the length of the week illustrate the avoidance of any mention of Scriptural authority. For example:

"The seven-day week is firmly entrenched and no one knows for certain where it came from... Perhaps the week was originally used to mark the phases of the moon and we have forgotten the connection." - Brown (p.2-3).

"A 7-day week of uncertain origin (perhaps traceable to the approximate phases of the moon or to the popularity of the number 7) was observed with the entirely Israelite feature of a sacred day of rest on the 7th day." - MacRae (p.1068).

"Our own Western 7-day week, one of the most arbitrary of our institutions, came into being from popular need and spontaneous agreement, not from a law or the order of any government... The number seven almost everywhere has had special charm. The Japanese found seven gods of happiness, Rome was set on seven hills, the ancients counted seven wonders of the world, and medieval Christians enumerated seven deadly sins." - Boorstin (p.13).

Table 1: A Representative List of Calendar Systems

Calendar Length of Week Period of Use Source*
Hebrew 7 14th century B.C. P
Macedonian none 9th century B.C. P
Chaldeans 7 747-734 B.C. P
Egypt 10, none   R
Babylon 10 625-316 B.C. P
Assyria 6   R
Zoroastrian none 389 B.C. P
Greek 10   P
Rome 8, 10   P
Islamic 7 622 A.D. - Present P
West Africa 4   R
Central Asia 5   R
French Republican 10 1792-1806 A.D. P
Russia 5 1929-1930 A.D. P
Gregorian 7 1582 - Present  
* The source is either Parise (p. 5,8) = P; or Robson (p.596) = R. The sources were in conflict for some items.

Astronomical bodies are frequently mentioned for the origin of the seven-day week: Sun (Sunday), Moon (Monday), Mars (Tuesday), Mercury (Wednesday), Jupiter (Thursday), Venus (Friday), Saturn (Saturday). It is true that the days are presently named after these celestial lights, which are themselves named for Greek deities. This simply fits man's usual pattern of naming discoveries and inventions after his own gods. However, the idea that the week's length originated from these bright lights must be challenged. Consider the case of the planet Venus. It was seen in antiquity as two separate objects and was given two names: the morning star (Phosphorus) and the evening star (Hesperus). It is unknown whether the ancients realised that both of these lights were in reality a single object. It would seem that Venus could easily have been named for two separate days of the week, and the same is true for Mercury. If the week was first defined by wandering lights in the sky, there should be at least nine weekdays! Instead, it is more likely that the already-existing pattern of seven-days was later superimposed with planetary names.

Old Testament Israel used a lunisolar calendar that is still followed today for Hebrew religious days. The Islamic nations also use a lunar calendar and carefully observe the phases of the moon. It is to be expected then that the moon is often appealed to for the definition of the week. After all, the quarter phases of the moon are "about" a week apart. Actually, the moon's synodic period is 29.53 days. This natural cycle comes close to an integral number of sevens, but is certainly not an exact 28 days. If used in establishing a lunar week, it would have been more precise to insert three weeks into a lunar cycle, each being 10 days in length! Also, lunar phases do not really provide a convenient visual calendar. The first quarter moon is overhead at sunset, the full moon rises at sunset, the third quarter is not seen until midnight, and the new moon (or waxing crescent) is barely seen at all. As with the planets, the cycle of moon phases was most likely used as a framework which was assigned to an already-existing seven-day pattern.


It is with hesitation that one attempts a discussion of calendar systems with their inherent complexity. However, their study shows that the enduring seven-day week is a strong testimony to the reliability of Scripture and the work of Creation. The final word has not been written on calendars; new proposals have arisen on reform. The seven-day week and the variable lengths of months are unsatisfactory to some people. Merchants in particular would like holidays on the same week day each year. One popular suggestion is called the 'International Fixed Calendar'. Each year would be 364 days long, or 52 weeks exactly. One's birthday would then always fall on the same day of the week. Each of the 13 months would also contain a Friday the 13th! There would be an extra 365th day (two during leap year) that did not belong to any week. This added day would bear no month or weekday designation. History predicts that such a system, even though diverging from the seven-day week by just one or two days a year, would be doomed to failure.

Several suggestions arise for further study on the subject of weekly time reckoning. Can the seven-day week be traced back through early extra-Biblical literature just as Flood traditions have been? In what ways is the seven-day week an optimum time interval for our physical and mental well-being?

Who is promoting calendar reform in our day and what are the real motives? What upper limit does the seven-day week and the tidal-frictional slowing of the earth's rotation place on the age of the earth?


  • Abrahams, I. (1903). 'Time: A Dictionary of the Bible, Volume IV'. Charles Scribner's Sons, New York.
  • Alter, D. C. H. Cleminshaw, J. G. Phillips. (1974). 'Pictorial Astronomy'. Thomas Y. Crowell Company, New York.
  • Boorstin, D. J. (1983). 'The Discoverers'. Random House, New York.
  • Brown, H. (1978). 'Man and the Stars'. Oxford University Press, Oxford.
  • MacRae, G. W. (1967). 'New Catholic Encyclopedia, Volume II'. McGraw-Hill Book Company, New York.
  • Moyer, G. (1982). 'The Gregorian Calendar'. Scientific American 246:144-152.
  • Parise, F. (1982). 'The Book of Calendars'. Facts on File, Inc., New York.
  • Robson, C.A. (1983). 'Calendar. New Encyclopedia Britannica, Volume 3'. Encyclopedia Britannica Inc., Chicago.
  • Van Till, H. (1986). 'The Fourth Day'. William B. Eerdmans Publishing Company, Grand Rapids, MI.
  • Don B. DeYoung, Ph.D.
  • Physical Science Department
  • Grace College
  • Winona Lake, IN 46590.

Source: 'Creation Research Society Quarterly'