9/2012 It's all in the stars

Post hoc ergo propter hoc

I was reading the book "Astrology, belive it or not ?" by S. Balachandra Rao (Pub.: Navakarnataka Books, Bangalore, India). People who study formal logic, are aware of the term "Post hoc ergo propter hoc". Post hoc ergo propter hoc, Latin for "after this, therefore because of this," is a logical fallacy (of the questionable cause variety) that states, "Since that event followed this one, that event must have been caused by this one." A subtle variant of this fallacious wisdom is the fallacy called "cum hoc ergo propter hoc", in which the chronological ordering of a correlation is insignificant, yet the events are given a cause-effect relationship.

It is commonly seen that we often observe two unrelated events and conclude that one caused the other. This class of examples is sometimes called the "Rooster Syndrome": "believing that the rooster’s crowing causes the sun to rise". Another example of such fallacious logic lies in statements like :: "A black cat crossed my path, so I missed the train" or in the conclusion that "Bob was in the same train as Alan, so Bob is Alan's murderer".

The most ridiculous usage of "Post hoc ergo propter hoc" is in astrology. The bunkum extends to correlating the relentless motion of planets, to earthly phenomena. A planet's position, as seen from the earth, against the backdrop of some arbitrarily chosen bunch of stars decides whether your favourite horse will win the jackpot or not. Planets have always been moving in the skies. People have always been betting on horses. Why not link these two phenomena ? You dont need to know Latin, or know formal logic, to see the farce called astrology.

The day of the week, when a child is born, will decide whether or not he will win the Nobel Prize. "Einstein was born on a Wednesday, so he won the Nobel Prize". How about all those who were born like Einstein, but did not get the Nobel ? Or, all those who got the Nobel Prize but were not born on Wednesday ? Never mind the hard work the surgeon puts in, to save a life. The patient died because the stars were not in the right place or in the mood to let him survive. "It's all in the stars", says the all-knowing astrologer, to console the dead man's widow. By interspersing their discourses with astronomic jargon and mumbo jumbo they can confuse even the staunchest of astronomers.

When will people learn to use common sense ?



8/2012 When was JC born ? A sequel

My blog entry 3/2012 pondered "when was Jesus Christ born?". This entry is a sequel to the question posed in 3/2012.

This article is about a simple problem, not related to any religion or belief. The problem may be simply stated as :: chronologically speaking, which came first, Jesus Christ's (JC) birth, or the start of the Christian Era (Anni Domini) ? If JC was born on Christmas Day (25 Dec.), why does the New Year in Christian Era (Anno Domini) start a whole week later ? So, JC's birthday cannot be given in AD. If AD started before JC's birthday, JC was not even born when AD started. Sounds perplexing. The answer to this enigma is not easy, or fool proof.

Between the two possibilities, the option where JC was born "before" the AD era (CE), seems to be more plausible. The option that the AD era started before JC's birth is clearly a contradiction. But, this is still a conjecture.

The abbreviation A.D. is short for "Anni Domini Nostri Jesu Christi", i.e., "in the year of Our Lord Jesus Christ". Since Muslims, Jews, etc., may not be entirely comfortable with this, the designation "A.D." is now sometimes replaced by the more neutral C.E. (for "Common Era"), and instead of B.C. ("Before Christ") B.C.E. (for "Before Common Era") is sometimes used. The Gregorian Calendar is the calendar which is currently in use in all European and European-influenced countries, and Dionysius Exiguus's system of numbering years A.D. has endured to the present time. The system of numbering years A.D. (for "Anni Domini") was instituted in about the year 527 A.D. by the Roman abbot Dionysius Exiguus, who reckoned that the Incarnation of Jesus had occurred on March 25 in the year 754 a.u.c., with his birth occurring nine months later. Thus the year 754 a.u.c. was designated by him as the year 1 A.D. It is generally thought that his estimate of the time of this event was off by a few years (and there is even uncertainty as to whether he identified 1 A.D. with 754 a.u.c. or 753 a.u.c.).

Originally the Romans numbered years ab urbe condita (auc) , that is, "from the founding of the city" (of Rome, where much of the character of the modern world had its beginnings). Following his conquest of Egypt in 48 B.C. Julius Caesar consulted the Alexandrian astronomer Sosigenes about calendar reform (since the a.u.c. calendar then used by the Romans was completely inadequate to the needs of the emerging empire, which Caesar was poised to command, briefly as it turned out). The calendar which Julius Caesar adopted in the year 709 a.u.c. (what we now call 46 B.C.) was identical to the Alexandrian Aristarchus' calendar of 239 B.C., and consisted of a solar year of twelve months and of 365 days with an extra day every fourth year. It is unclear as to where or how Aristarchus arrived at this calendar, but one may speculate that Babylonian science was involved. 1 January was the established as the start of the year in Rome at the time of the reign of Julius Caesar. That date had apparently no religious significance in ancient Rome. It is said that Julius Caesar wanted to start the year on the vernal equinox or the winter solstice, but the Senate, which traditionally took office on January 1st, wanted to keep January 1st as the start of the year, and Caesar yielded in a political compromise.

To complicate matters further New Year's Day, the first day of the new year, was celebrated in different countries, and sometimes by different groups of people within the same country, on either January 1, March 1, March 25 or December 25. January 1 seems to have been the usual date but there was no standard observed. With the introduction of the Gregorian Calendar in Britain and the colonies New Year's Day was generally observed on January 1.

Thus 1 January has no relationship to the birth of JC. 1 January has no astronomical significance either. There are indications that many years before Caesar, March used to be the start of the year, since the months September-December are named after the Latin names for 7-10.

The question has been raised as to whether the first Christian millennium should be counted from 1 A.D. or from the year preceding it. According to Dionysius the Incarnation occurred on March 25th of the year preceding 1 A.D. (with the birth of Jesus occurring nine months later on December 25th), so it is reasonable to regard that year, rather than 1 A.D. as the first year of the Christian Era. In that case 1 A.D. is the second year, and 999 A.D. is the 1000th year, of the first Christian millennium, implying that 1999 A.D. is the final year of the second Christian millennium and 2000 A.D. the first year of the third.

We don't know the precise date on which Jesus was born. Celebrating his birth on 25 December is an old Christian tradition, but he might just as well have been born on any other date. There is a popular theory that Christians chose 25 December because there was already a pagan celebration of the winter solstice on or near that date, and Christians then simply gave that date a new significance. But in Christianity it does have significance. Jesus (like all Jewish boys) was circumcised exactly one week after his birth. Since we celebrate his birth on 25 December, his circumcision is celebrated on 1 January. This also means that 1 January is the celebration of Jesus' name; according to the Gospel of Luke, "On the eighth day, when it was time to circumcise him, he was named Jesus, the name the angel had given him before he had been conceived." (Luke 2:21)

The year of birth of Jesus can be estimated using two independent approaches: one based on the nativity accounts in the gospels of Matthew and Luke, the other by working backwards from the date of the start of his ministry, when according to the Gospel of Luke he was about thirty years old. Most scholars assume a date of birth between 6 and 4 BC. This strengthens the theory that CE started much after JC's birthday.

It is true that Christ's birthday would be an appropriate date to celebrate New Year, and in the Middle Ages that was not uncommon. In countries like Denmark, the new year started on 25 December before the 13th century (although there are also historical documents that use other dates). But, of course, calendars are easier to manage if the new year starts on the first day of a month rather than the 25th. It is unclear why the Romans chose to move the start of the year to January.

Note : The above article is a collection of statements found in different, scattered sources on the w-w-web. There is no way to certify the authenticity of these statements. There is still a considerable amount of debate on the origin of calendars and eras. The above article should not be considered as a definite answer to any of the issues involved.



7/2012 Don. Knuth answers your questions

An hour long video where Prof. D E Knuth takes questions live.


The video runs for 1h 09 min. and is a 186 MB mp4 file.


6/2012 Don. Knuth unveils the next Tex

June 2010, Calfornia.

TUG 2010: TeX's 25th anniversary included a talk by Prof Donald Knuth on the design features of the next version of Tex which he is working on. Spiced with his characteristic sparks of humour, this is a must-see video for all TeX/LatEx lovers ::


The video runs for 33.43 minutes and comes as a 87.7 MB file in mp4 format.


PS I have downloaded the above file and can send it to genuine TeX/LaTeX practitioners (you bear the postage and copying costs)