The crystallographic meaning of the phrase "ab initio" is an old chestnut which
I ran into when writing a paper "Ab initio phasing of a 4189-atom protein structure at 1.2 A resolution".
Gerard B. heard me talk at Erice (2000) and later wondered aloud in his talk whether my use
of the term was appropriate since there are 5 ordered uranium atoms in the structure. My paper
was not I think the "falsely spectacular" one he referred to in his recent email, but a simple
demonstration of ARP/wARP. No anomalous signal was used at all, just a single dataset to
high resolution. His comment led me to refer in my paper to the definition of "ab initio" given
by Uson and Sheldrick (1999) Curr. Op. Struct. Biol. 9, 643-648.
With regard to Bill Scott's comment that "I'd use the dictionary, not social consensus" it should
be remembered that today's dictionaries are written with the broken usages selected by
previous generations. British dictionaries often define a "billion" as 10 to the power 12, but UK consensus
is very much in favour of the American usage, meaning 3 orders of magnitude less. (What happened
to "milliard"? The continent still uses it.) A key part of any science, after all, is creating a language
in which its discoveries can readily be understood.
If "ab initio" does indeed mean the same as "direct methods" then why use it? "Direct phasing" or
"phasing directly" seem simpler, but "ab initio" is the more time-honoured. A few years back
"atomic resolution" was another much-abused phrase, meaning anything up to about 2.4 Angstroms,
so it is worth discussing these issues from time to time to make sure the meanings are clearly
Gerard B. wrote
"More seriously, there seems to be a problem with using more than
one Latin expression these days ....."
I agree. The rules for the Oxford-Cambridge boat race are written in Latin (but of course), and there
was an unholy row (sorry for the pun) over whether "in statu pupillari" included graduate
students. Oxford won the argument, and 3 more races, with the unfortunate consequence
that both teams now consist of semi-professionals.
But perhaps the best reason for the enduring appeal of Latin was given by a professor in a short
story by Voltaire, from old memory:
Il faut expliquer ce qu'on ne comprend pas dans les langues on entend le moins.
Apologies in advance to French speakers out there.