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The day-year principle, year-day principle or year-for-a-day principle is a method of interpretation of Bible prophecy in which the word day in prophecy is symbolic for a year of actual time. It is used principally by the historicist school of prophetic interpretation. It is held by the Seventh-day Adventist Church, Jehovah's Witnesses, some Pentecostals and the Christadelphians. The day-year principle is also used by the Bahá'í Faith.
- 1 Biblical basis
- 2 History
- 3 Christian Historicist Application
- 4 Baha'i Application
- 5 See also
- 6 References
- 7 Further reading
- 8 External links
Proponents of the principle, such as the Seventh-day Adventists, claim that it has three primary precedents in Scripture:
- Numbers 14:34. The Israelites will wander for 40 years in the wilderness, one year for every day spent by the spies in Canaan.
- Ezekiel 4:5-6. The prophet Ezekiel is commanded to lie on his left side for 390 days, followed by his right side for 40 days, to symbolize the equivalent number of years of punishment on Israel and Judah respectively.
- Daniel 9:24-27. This is known as the Prophecy of Seventy Weeks. The majority of scholars do understand the passage to refer to 70 "sevens" or "septets" of years—that is, a total of 490 years.
This view was recognized by the Jews as seen in Daniel 9:24-27, and as seen in Jesus' use of the day-year principle in Luke 13 verses 31-33, and in the early church. The day-year principle was first used in Christian exposition in 380 AD by Tychonius, who interpreted the three and a half days of Revelation 11:9 as three and a half years, writing 'three days and a half; that is, three years and six months' ('dies tres et dimidium; id est annos tres et menses sex'). In the 5th century Faustus of Riez gave the same interpretation of Revelation 11:9, writing 'three and a half days which correspond to three years and six months' ('Tres et dimidius dies tribus annis et sex mensibus respondent), and in c. 550 Primasius also gave the same interpretation, writing 'it is possible to understand the three days and a half as three years and six months' ('Tres dies et dimidium possumus intelligere tres annos et sex menses'). The same interpretation of Revelation 11:9 was given by the later Christian expositors Bede (730 AD), as well as Anspert, Arethas, Haymo[disambiguation needed], and Berengaud (all of the ninth century). Primasius appears to have been the first to appeal directly to previous Biblical passages in order to substantiate the principle, referring to Numbers 14:34 in support of his interpretation of the three and a half days of Revelation 11:9. Haymo and Bruno Astensis "justify it by the parallel case of Ezekiel lying on his side 390 days, to signify 390 years ; — i. e. a day for a year. — ". Protestant Reformers were well established on the day/year principle and it was also accepted by many Christian groups, ministers, and theologians.
Others who expounded the Historicist interpretation are John Wycliffe, John Knox, William Tyndale, Martin Luther, John Calvin, Ulrich Zwingli, Phillip Melanchthon, Sir Isaac Newton, Jan Huss, John Foxe, John Wesley, Jonathan Edwards, George Whitefield, Charles Finney, C. H. Spurgeon, Matthew Henry, Adam Clarke, Albert Barnes, E. B. Elliot, H. Grattan Guinness, and Bishop Thomas Newton as exponents of this school.
Christian Historicist Application
490 year prophecy
Daniel 9 contains the Prophecy of Seventy Weeks. Even though neither the word "day" nor "year" are used in the text, historicist commentators and most Reformation theologians, interpret the 490 as years. For more information, see Prophecy of Seventy Weeks
1260 year prophecy
Historicist interpreters have usually understood the "time, times and half a time", "1,260 days" and "42 months" mentioned in Daniel and Revelation to be references to represent a period of 1260 years.
These time periods occur seven times in scripture:
- Daniel 7:25, "time, times and a half".
- Daniel 12:7, "time, times and a half".
- Revelation 11:2, "42 months".
- Revelation 11:3, "1260 days".
- Revelation 12:6, "1260 days".
- Revelation 12:14, "time, times and a half".
- Revelation 13:5, "42 months".
Historicists usually believe the "1,260 days" spanned the Middle Ages and concluded within the early modern or modern era. Although many dates have been proposed for the start and finish of the "1,260 days", certain time spans have proven to be more popular than others.. The majority of historicists throughout history have identified the "1,260 days" as being fulfilled by one or more of the following time spans:
- 312 AD to 1572: Battle of the Milvian Bridge/Vision of Constantine to St. Bartholomew's Day massacre
- 606 AD to 1866
- 538 AD to 1798: Siege of Rome to Napoleon's Roman Republic.
- 756 AD to 2016: Donation of Pepin to (presumed) fall of Papacy.
The Millerites, like the earlier Bible students of the Reformation and post-Reformation eras, and the Seventh-day Adventists,  understand the 1260 "days" to be the period from AD 538 to 1798 when the papacy ruled in Rome. This period began with the defeat of the Ostrogoths by the general Belisarius and ended with the successes of Napoleon of France; specifically, the capture of Pope Pius VI by general Louis Alexandre Berthier in 1798.
Robert Fleming writing in 1701 (The Rise and Fall of Rome Papal) stated that the 1260-year period should commence with Pope Paul I becoming a temporal pope in AD 758 which would expire in 2018. Adam Clarke writing in 1825 stated that the 1260-year period should commence with 755 AD, the actual year Pepin the Short invaded Lombard territory, resulting in the Pope's elevation from a subject of the Byzantine Empire to an independent head of state. The Donation of Pepin, which first occurred in 754 and again in 756 gave to the Pope temporal power of the Papal States. However, his introductory comments on Daniel 7 added 756 as an alternative commencement date. Based on this, 19th century commentators anticipate the end of the Papacy in 2016:
“As the date of the prevalence and reign of antichrist must, according to the principles here laid down, be fixed at A.D. 756, therefore the end of this period of his reign must be A.D. 756 added to 1260; equal to 2016, the year of the Christian era set by infinite wisdom for this long-prayed-for event. Amen and amen!" 
Of the five areas of the Bible which mention this timeline, only Revelation 11:9-12 adds a brief 3½ more years to the end of this 1260-year period. If added to 2016, this would bring us to the fall of 2019 for the commencement of the Eternal Kingdom. However, far more attention is paid by historicists to 2016 as the final end of the Papacy and the commencement of the Millennial rule than there is to 2019. This may be due in part, to uncertainty as to who or what the two witnesses of the Book of Revelation represent.
Though the end of the 1260 years will be marked by dramatic events, it will not instantly remove all the governments of the world. The Messianic Kingdom will be established in place of the former Roman Empire, and continue to expand until it has enveloped the remaining countries. The following is an excerpt from "the Covenanter", a Reformed Presbyterian publication (1857):
“The end of the 1260 years will not at once usher in the brightness of the Millennial day. It will be marked by some occurrence, by some grand movement of Providence—such as the violent, it may be, and sudden crushing of the Papal power, and that of the corrupt and oppressive monarchies of the Old World, and of the governments similar to them in spirit, if not in form, in the New-— by some event in the pagan world, in which a new era will take its rise: new and signally successful efforts for the conversion of the Jews—for the evangelization of the nations-—for the subjecting of the “kingdoms of this world” to the law and government of “the Lord and of his Christ.” A generation may pass, or more than one, before this work will be fully completed; but it will advance with large strides.” 
While Daniel 2:35 makes reference to the various world powers (represented as various metals) being “broken to pieces together”, the previous verse (v.34) portrays the Eternal Kingdom coming as “a stone cut from a mountain without hands” and striking a statue (symbolizing the successive world empires) on its feet first. Most adherents of the day-year principle, interpret these feet “that were of iron and clay,” as denoting the nations descended from and occupying areas of the former Roman Empire. The dominions of all the empires and nations are expected to be crushed simultaneously, but the end of “life” or existence of the Roman derived countries will precede that of the other nations of the world.
The length of time for this world-wide expansion to complete is indicated in Daniel 7:12, which adds “As concerning the rest of the beasts, they had their dominion taken away: yet their lives were prolonged for a season and time.” Henry Folbigg (1869) elaborated on this verse:
It is here predicted that after the destruction of the papal beast, “the rest of the beasts,” by which I understand the Pagan, Mahometan, Hindoo, Chinese, and other empires, “ will have their dominion taken away,” that is, they will gradually lose their dominion, perhaps be conquered and lose their heathen rulers— “ but their lives ”—the existence of various corrupt "and unchristian principles, “ will be prolonged for a season and a time,” which, if intended to be taken in the usual prophetic and symbolic sense would indicate a period of 450 years. This would extend far into the Millennium, and therefore although we may and should look for, and hasten the coming of great and beneficial changes, we are not to expect universal civilization in a day, nor the conversion of the world in a year—but rather the gradual yet more rapid spread of the gospel and the spiritual reign of Christ and his saints—of Christ and his Church for 1,000 years.
2300 year prophecy
The distinctly Seventh-day Adventist doctrine of the divine investigative judgment beginning in 1844, based on the 2300 day prophecy of Daniel 8:14, relies on the day-year principle. The 2300 days are understood to represent 2300 years stretching from 457 BC, the calculated starting date of the 70 weeks prophecy based on the 3rd decree found in Ezra, to 1844. The prophecy of 2300 days in Verse 14 plays an important role in Seventh-day Adventist eschatology. The Seventh-day Adventist Church traces its origins to the William Miller, who predicted that the second coming of Jesus would occur in 1844 by assuming that the cleansing of the Sanctuary of Daniel 8:14 meant the destruction of the earth and applying the day-year principle. The 2300 days are interpreted as 2300 years, starting at the same time as the Prophecy of Seventy Weeks found in Chapter 9, on the grounds that the 70 weeks were "decreed" (actually "cut off") for the Jewish people from the 2300-day prophecy. This beginning year is calculated to be 457 BC (see details here), so that the end of the 2300 years would have been in 1844. Although the Millerites originally thought that 1844 represented the end of the world, those who later became Seventh-day Adventist reached the conclusion that 1844 marked the beginning of a divine pre-advent judgment called "the cleansing of the sanctuary". It is intimately related to the history of the Seventh-day Adventist Church and was described by the church's prophet and pioneer Ellen G. White as one of the pillars of Adventist belief.
Baha'i Recognition of the 2300 Day-Year Prophecy
Baha'is also recognize the Day-Year Principle and use it in understanding prophecy from the Bible. In the book, Some Answered Questions, `Abdu'l-Bahá outlines a similar calculation for the 2300-year prophecy as given in the Christian section above. By applying the day-year principle, he demonstrates that the fulfillment of the vision of Daniel occurred in the year 1844, the year of the Báb's declaration in Persia i.e. the starting date of the Baha'i Faith. This is the same year that the Millerites predicted for the return of Christ, and Baha'is believe that William Miller's methodologies were indeed sound.
The prophecy states "For two thousand three hundred days; then the sanctuary shall be cleansed." (Daniel 8:14) Baha'is understand the "cleansing of the sanctuary" to be the restoration of religion to a state in which it is guided by authorities appointed by its Founder rather than by people who have appointed themselves as the authority. (The leaders of Sunni Islam were self-appointed; the first 12 leaders of Shia Islam had been appointed through a chain of succession going back to Muhammad, but that chain ended after 260 years—see next section below.) Thus Baha'is believe that divinely-guided religion was re-established in 1844 with the revelation of the Báb, continued through the revelation of the Baha'i founder (Baha'u'llah) and continues today through their Universal House of Justice, elected according to the method described by Baha'u'llah.
Although Christians have generally expected their Messiah to appear somewhere in Judeo-Christian lands, Baha'is have noted that Daniel himself was in Persia at the time the prophesy was made. He was in Shushan (modern day Susa or Shūsh, Iran), when he received his prophetic vision (Daniel 8:2). The Bab appeared 2300 years later in Shiraz, about 300 miles away from where Daniel's vision occurred.
Convergence of 1260-Day Prophecy and the 2300-Day Prophecy
The year 1260 was significant in Shia Islam, independently of any Biblical reference. The Shia branch of Islam followed a series of 12 Imams, whose authority they traced back to Muhammad. The last of these disappeared in the Islamic year 260 AH. According to a reference in the Qur'an, authority was to be re-established after 1,000 years. For this reason, there was widespread anticipation among Shi'ites that the 12th Imam would return in Islamic year 1260 AH. This is also the year 1844 AD in the Christian calendar. Thus both the Millerites and the Shi'ites were expecting their Promised One to appear in the same year, although for entirely independent reasons.
Therefore, Baha'is understand the 1260-day prophecies in both Daniel and in the Book of Revelation as referring to the year 1260 of the Islamic calendar  which corresponds to the year 1844 AD, the year the Báb pronounced himself to be a Messenger of God and the year that the Baha'i Faith began.
Day-Year Principle in Revelation 9:15 (391 Days)
Baha'is have also applied the Day-Year principle to Rev. 9:15 which states, "And the four angels were loosed, which were prepared for an hour, and a day, and a month, and a year, for to slay the third part of men."
The slaying of "the third part of men" was interpreted by some Christian scholars to refer to the fall of the Eastern Orthodox part of Christianity, centered on Constantinople in the year 1453 AD. (The other two-thirds being the Western Christian world, centered on Rome, and the southern part of the Christian world in North Africa, which was already under the dominion of Islam long before 1453.) Using the day-year principle, the formula gives 1+30+360 days = 391 days = 391 years after 1453. Adding 391 years to 1453 brings the prediction again to 1844, the same year as the 2300 day prophecy of Daniel 8.
Theoretically, this prophecy could be taken one step further, since there are accurate records of the dates of the start and end of battle for Constantinople. If "the hour" is taken to be 1/24th of a day, then, by the day-year principle, it would equate to 1/24 of a year i.e. 15 days. Since the battle of Constantinople lasted for several weeks, it is not possible to pin down the exact starting day of this 391-1/24-year prophecy, but if the formula is followed to this degree, it suggests the prophecy's fulfillment should have occurred sometime in May or June 1844.
Day-Year Principle in Daniel 12: 1290- and 1335-Day Prophecies
In addition, Baha'is have applied the Day-Year principle to the two prophecies at the end of the last chapter of Daniel concerning the 1290 days (Dan 12:11) and the 1335 days (Dan 12:12). The 1290 days is understood as a reference to the 1290 years from the open declaration of Muhammad to the open declaration of Baha'u'llah. The 1335 days is understood to be a reference to the firm establishment of Islam in 628 AD to the firm establishment of the Baha'i Faith (the election of its Universal House of Justice) in 1963 AD.
- Abomination of Desolation
- Bible prophecy
- Historicism - The school of prophetic interpretation which uses the day-year principle.
- Summary of Christian eschatological differences
- Investigative judgment
- Daniel's Vision of Chapter 7
- Daniel's Vision of Chapter 8
- Day-age creationism
- Prophetic Year
- Post Tribulation Rapture
- Prophecy of Seventy Weeks
- Seventh-day Adventist eschatology
- The Two Witnesses
- Roberts, Robert, Thirteen Lectures On The Apocalypse, Lecture 10, 1921.
- "Seventh-day Adventists Believe - An Exposition of the Fundamental Beliefs of the Seventh-day Adventist Church, 2nd edition". Ministerial Association, General Conference of Seventh-day Adventists. 2005. p. 48.
- Jon Paulien, "A New Look at the Year-Day Principle", talk at the 2008 Evangelical Theological Society meetings
- Froom, L. E. (1950). Prophetic Faith of Our Fathers. 1 & 2. Review and Herald. pp. 889 and 124.
- Froom, L. E. (1950). Prophetic Faith of Our Fathers 1. Review and Herald. pp. 170, 174–76.
- Elliott, EB (1862). Horae Apocalypticae III (fifth ed.). p. 279.
- Elliott, EB (1862). Horae Apocalypticae III (fifth ed.). p. 280.
- Prismasius; Elliott, EB (1862). Horae Apocalypticae III (fifth ed.). p. 280.
More Scripturae loquentis utentes, quod dictium legius de quadraginta diebus quibus exploratores terram Channan circuierunt, anus pro die reputabitur; ut hic, versa vice, dies pro anno positus agnoscatur
- Elliott, EB (1862). Horae Apocalypticae III (fifth ed.). p. 281.
- du Ion, Francois (1596). The Apocalyps. p. 124.
- Nigrinus. Antichrists Grundtliche Offenbarung. p. fils 28v,29r.
- Burr, Aaron. The Watchman's Answer to the Question, What of the Night. p. 21.
- S. Gregg, "Revelation: Four Views," Nashville: Thomas Nelson Pub, 1997, p. 34.
- Seventh-day Adventists Believe (2nd ed). Ministerial Association, General Conference of Seventh-day Adventists. 2005. pp. 184–185. ISBN 1-57847-041-2.
- Leroy Edwin Froom, The Prophetic Faith Of Our Fathers, volume II (1948) pages 784, 787; volume III (1946) pages 744-745; volume IV (1982) pages 392, 395-397, 399-400
- Edward Bishop Elliott in his four-volume Horae Apocalypticae regarded the prophetic periods as representing the same temporal period, 606 - 1866CE. His view of the symbolic nature of the day-year principle was similar to the 'man as microcosm' argument; that a day in the life of a man could be likened to a year in the life of the wider world. Among his illustrations for this were Ezekiel 16 where the youth of a woman is likened to the growing in maturity of the Jewish people. (see Edward Bishop Elliott Horae Apocalypticae London: Seeley, Jackson & Halliday 5th ed (1862) Vol 3 p. 263) Similarly, the sabbath as a day for the individual is mirrored in the seventh fallow year of an agrarian society. Likewise, Ezekiel 4:1-7 where the prophet lies prostrate for a number of days to mirror the number of years of iniquity of Judah and Israel. "I have appointed thee each day for a year." He says another interesting, if problematic, illustration is Isaiah 20:2-3 where Isaiah appears to walk naked for three years. Elliott suggests that his prophetic act would have lasted three days as a sign of what the Assyrians would accomplish three years thence.
- The Seventh-day Adventist Bible Commentary, vol. 4 (Washington, DC: Review and Herald, 1955), p. 880. "A time, times, and an half. That is, the 1260-year period, A.D. 538-1798, which is first introduced in ch. 7:25."
- LeRoy E. Froom “Prophetic Faith of our Fathers” Washington D.C.: Review and Herald Publishing Association (1946) Vol. 3 page 219 citing Bishop Thomas Newton (1766): “But as the Pope did not acquire temporal power till 756, it is more probable that this delays the terminus until 1260 years from that date”
- http://www.adventistbiblicalresearch.org/documents.htm#prophecy, What Prophecy Means to This Church, Frank B. Holbrook, Ministry, July 1983
- The Great Controversy by Ellen White, p266. "Chap. 15 - The Bible and the French Revolution"
- Seventh-day Adventists Believe (2nd ed). Ministerial Association, General Conference of Seventh-day Adventists. 2005. pp. 184–185. ISBN 1-57847-041-2.
- Adam Clarke ”The Holy Bible” New York: Lane and Scott (1850) Vol. IV, Introduction to Chapter VII. Page 592 “It will be proper to remark that the period of a time, times, and a half, mentioned in the twenty-fifth verse are the duration of the dominion of the little horn that made war with the saints, (generally supposed to be a symbolic representation of the papal power,) had most probably its commencement in A.D. 755 or 756, when Pepin, king of France, invested the pope with temporal power. This hypothesis will bring the conclusion of the period to about the year of Christ 2000, a time fixed by Jews and Christians for some remarkable revolution; when the world, as they suppose, will be renewed, and the wicked cease from troubling the Church, and the saints of the Most High have dominion over the whole habitable globe.“
- Freeborn Garretson Hibbard “Eschatology: Or, The Doctrine of the Last Things” New York: Hunt & Eaton (1890) page 84
- D. D. Whedon “The Methodist Quarterly Review” New York: Carlton & Porter (1866) Article V page 256
- Daniel 7:25, Daniel 12:7, Revelation 11:2-3, Revelation 12:6,14 and Revelation 13:5
- The 3½ days follow the 42 months or 1260 days (representing years) mentioned in verses 2 and 3.
- Thomas Williams “The Cottage Bible and family expositor” Hartford: D.F. Robinson and H.F. Sumner (1834) Vol.2 page 1417: “Mr. Lowman, though an earlier commentator, is (we believe) far more generally followed; and he commences the 1260 days from about 756, when, by aid of Pepin, King of France, the Pope obtained considerable temporalities. This carries on the reign of Popery to 2016 or sixteen years into the commencement of the Millennium, as it is generally reckoned.”
- James L Willson (editor) “The Covenanter” Philadelphia: William S. Young (1857) Vol. 13 page 238
- George D'Oyly “The Holy Bible According to the Authorized Version” London: Society for Promoting Christian Knowledge. Gilbert & Rivington. (1830) Volume II. Daniel, chapter II: The Roman empire therefore is represented in a double state; first, with the strength of iron, conquering all before it, "his legs of iron;" and then weakened and divided by the mixture of barbarous nations, "his feet part of iron and part of clay." The Roman empire was afterwards divided into ten lesser kingdoms, the remains of which are subsisting at present.
- William Greenfield “Pillar of Divine Truth” London: Samuel Bagster (1831) Page 232: “The Roman empire became weakened by a mixture of barbarous nations, by the incursions of whom it was torn asunder about the fourth century after Christ, and at length divided into ten kingdoms, answering to the ten toes of the image, and the ten horns of the beast. The ten kingdoms into which the western Roman empire was divided were, primarily, according to Machiavel and Bp. Lloyd, 1. The Huns in Hungary, A. D. 356. 2. The Ostrogoths in Moesia, 377. 3. The Visigoths in Pannonia, 378. 4. The Sueves and Alans in Gascoigne and Spain, 407. 5. The Vandals in Africa, 407. 6. The Franks in France, 407. 7. The Burgundians in Burgundy, 407. 8. The Heruli and Turingi in Italy, 476. 9. The Saxons and Angles in Britain, 476. 10. The Lombards first, upon the Danube, 526, and afterwards in Italy. Though the ten kingdoms differed from these in later periods, and were sometimes more or less, yet they were still known by that name.”
- Daniel 7:11, 12: “I beheld even till the beast was slain, and his body destroyed, and given to the burning flame. As concerning the rest of the beasts, they had their dominion taken away: yet their lives were prolonged for a season and time.”
- James Bicheno “The Restoration of the Jews” London: Bye and Law (1800) Page 48: “The destruction is to begin at the toes of the image, the kingdoms into which the Roman empire has been divided.”
- Henry Folbigg “The Great Epoch” London: Longmans, Green, Reader, and Dyer.(1869) Pages 134-135
- Seventh-day Adventists Believe (2nd ed). Ministerial Association, General Conference of Seventh-day Adventists. 2005. pp. 358–359. ISBN 1-57847-041-2.
- William Shea, " PDF". Journal of the Adventist Theological Society 12:1 (Spring 2001), p89–96
- White, E.G., "Counsels to Writers and Editors," pp. 30, 31 (Old Landmarks)
- Venden, Morris, 1982, "The Pillars", Pacific Press, p. 13-15
- Some Answered Questions. US Baha'i Publishing Trust. 1990. p. 42.
- The Prophecies of Jesus. OneWorld Publications, Ltd, Oxford, UK. 1991. p. 82.
- The Covenant of Baha'u'llah. George Ronald Publisher, Ltd, Oxford, UK. 1992. pp. 1–441.
- Thief in the Night, William Sears, George Ronald Publishers, Oxford, England, 1992 Chap 18, pg 73
- Dawn of Mount Hira. George Ronald, Oxford, UK. 1976. p. 58.
- Some Answered Questions. US Baha'i Publishing Trust. 1990. p. 46.
- William Sears, Thief in the Night, Part 1, Chap 6, pg 24 George Ronald Publisher, Oxford, UK 1961
- H. Grattan Guinness, The Approaching End of the Age (1880, Hodder and Stoughton, London) at http://archive.org/stream/approachingendof00guin#page/662/mode/2up
- Michael Paget Baxter, The Coming Battle (W. Harbert, Philadelphia, 1860)
- Michael Sours, The Prophecies of Jesus, Appendix 7, pgs 201-204 (One World Publications, Oxford, UK, 1991)
- Moon, Jerry. "The Year-Day Principle". AtIssue. SDAnet.
- William H. Shea, "Year-Day Principle – Part 1" (p67–104) and Part 2 (p105–110) in Selected Studies in Prophetic Interpretation; Daniel and Revelation Committee Series, vol 1. Maryland: Biblical Research Institute/Review and Herald, rev edn, 1982. Part 1 has been called "arguably the [Adventist] church’s best scholarly defense of the day-year principle."
- Gerhard F. Hasel, “The Hebrew Masculine Plural for ‘Weeks’ in the Expression ‘Seventy Weeks’ in Daniel 9:24” (AUSS 31/2  105-18.
- Frank W. Hardy, “The Hebrew Singular for ‘Week’ in the Expression ‘One Week’ in Daniel 9:27” (AUSS 32/3  197-202
- Desmond Ford, Daniel appendix (note the author has since changed his position – see below)
- Kai Arasola, The End of Historicism (PhD thesis). This is a history, which includes the decline of use of the day-year principle