Les voyes de prudence

What the passage says

Forster wrote from France in May 1644. The plaintext names no person, place or title, so the addressee is inferred, not established. Karen Britland's abstract says Henrietta Maria, at Exeter, ill, pregnant, and deciding whether to flee to France, made a related request a few days later, which makes her a plausible addressee, not a certain one. Whether Forster composed the counsel or relayed a confessor's is open.

How it was read

The cipher is a mixed letter-and-number homophonic substitution: 34 symbols over 207 tokens, in 37 comma-separated words. Character n-gram hill climbing went nowhere at that length. A beam search over a French lexicon with 17th-century spellings, constrained only by same-symbol-same-letter, produced most of the key in one run; a dozen symbols were then fixed by hand. The 16 letter-symbols map to 16 distinct plaintext letters, and the 18 number-symbols to 16. A Codex agent re-applied the key mechanically and reproduced the reading. Everything is reproducible from the published files.

Earlier readings

According to Karen Britland's account to Robert Pitt, George Lasry supplied a decipherment after her 2013 article, and Norbert Biermann reached the same solution independently. Pitt published his own key a few hours before ours on 14 September 2026. Pitt's key and ours were reached separately and are identical; the earlier reading Britland passed on differs in a few words.

Reading the columns

Left: the ciphertext in Tomokiyo's transcription of Britland's printed text; commas are word breaks, and the two passages Forster left in clear are in italic. Middle: the key's output in the letter's own spelling, then modernised. Right: an English translation. Square brackets mark the three places where the key's output needs repair; the symbols concerned are marked in the ciphertext. No image of the manuscript is online, so whether those slips are Forster's or a transcriber's is not known.

The passage

One page, one side; cipher with two clear passages and the date

Ciphertext

d c t g p 4 30 q 30 19 x 30 f 16 2 50 a 0 40 12 20 30 y 30 c 2 7 0 u 4 t 88 30 0 l p a d 2 30

ie vous en responds et mesmes dans

c 0 x l 2 d e c 0 40 7 2 y 0 20 n 2 12 50 16 s t 90 20 0 t 2 14 x a 30 c 2 u 0 t b 80 2 x 30 s g 0 x a 2 90 20 30 a 0 t q 2 90 16 30 20 12 s t q 0 l 30 2 20 30 s 50 20 2 30 d 0 y s 30 20 2 19 n p d l 0 4 a 16 2 30 30 t y c 30 x 5 20 4 19 7 40 4 12 l 16 70 d g 0 90 4 20 c p u 30 80 50 16 y c d q 4 8 16 s 19 a 2 40 30 s x 40 0 20 30 d 12 2 x y s 30 20 80 0 x 4 c 30 50 7 0 30 s x 70 20 2 l 0 40

et mesurer a cela sil est meilleur d'agir, ou de soupir 13. de may. 1644

French

Il ny a aucun subiet de scrupule de manquer a Dieu,

ie vous en responds et mesmes dans

les reigles de perfection. Prenez s[e]ulement les voyes de prudence p[o]ur concerver votre vie, pour en faire a Dieu un plus grand sacrifi[c]e par la multiplication des vos services pour le salut de vos freres;

et mesurer a cela sil est meilleur d'agir, ou de soubir. 13 de may 1644

Modernised

Il n'y a aucun sujet de scrupule de manquer à Dieu, je vous en réponds, et même dans les règles de perfection. Prenez seulement les voies de prudence pour conserver votre vie, pour en faire à Dieu un plus grand sacrifice par la multiplication de vos services pour le salut de vos frères ; et mesurer à cela s'il est meilleur d'agir ou de subir.

English

There is no cause for scruple about failing God, I answer to you for it, even by the rules of perfection.

Only take the ways of prudence to preserve your life, so as to make of it a greater sacrifice to God through the multiplication of your services for the salvation of your brethren; and measure by that whether it is better to act or to endure.

13 May 1644

Notes

Word 13, prenez s[e]ulement: cipher a (d) where 2 (e) is needed. A handwritten 2 and a are easily confused.
Word 16, p[o]ur: 16 (i) where s (o) is needed.
Word 27, sacrifi[c]e: g (y) where q (c) is needed; g and q are confusable in hand.
Word 17, conceruer: the key gives concerver, a spelling attested in period documents, so it is not repaired.
The last clear word is soupir in Tomokiyo's transcription and in Britland's printed text, but soubir in her abstract, that is subir, to endure. “To act or to endure” is the better reading.
Word breaks inside cipher words are unmarked: descrupule, manquera (manquer a), lesreigles, prenezseulement, lesvoyesde, enfaire, parla, lesalut.

The 37 cipher words with the key's raw output

Word	Cipher symbols	Key output	Reading
1	d c	il	il
2	t g	ny	ny
3	p	a	a
4	4 30 q 30 19	aucun	aucun
5	x 30 f 16 2 50	subiet	subiet
6	a 0 40 12 20 30 y 30 c 2	descrupule	descrupule
7	7 0	de	de
8	u 4 t 88 30 0 l p	manquera	manquera
9	a d 2 30	dieu	dieu
10	c 0 x l 2 d e c 0 40	lesreigles	lesreigles
11	7 2	de	de
12	y 0 20 n 2 12 50 16 s t	perfection	perfection
13	90 20 0 t 2 14 x a 30 c 2 u 0 t b	prenezsdulement	prenezs[e]ulement
14	80 2 x 30 s g 0 x a 2	lesuoyesde	lesuoyesde
15	90 20 30 a 0 t q 2	prudence	prudence
16	90 16 30 20	piur	p[o]ur
17	12 s t q 0 l 30 2 20	conceruer	conceruer
18	30 s 50 20 2	uotre	uotre
19	30 d 0	uie	uie
20	y s 30 20	pour	pour
21	2 19 n p d l 0	enfaire	enfaire
22	4	a	a
23	a 16 2 30	dieu	dieu
24	30 t	un	un
25	y c 30 x	plus	plus
26	5 20 4 19 7	grand	grand
27	40 4 12 l 16 70 d g 0	sacrifiye	sacrifi[c]e
28	90 4 20 c p	parla	parla
29	u 30 80 50 16 y c d q 4 8 16 s 19	multiplication	multiplication
30	a 2 40	des	des
31	30 s x	uos	uos
32	40 0 20 30 d 12 2 x	seruices	seruices
33	y s 30 20	pour	pour
34	80 0 x 4 c 30 50	lesalut	lesalut
35	7 0	de	de
36	30 s x	uos	uos
37	70 20 2 l 0 40	freres	freres

The key, by plaintext letter

Plain	Cipher symbols
a	p, 4
b	f
c	q, 12
d	a, 7
e	0, 2
f	n, 70
g	e, 5
i	d, 16
l	c, 80
m	u
n	t, 19
o	s
p	y, 90
q	88
r	l, 20
s	x, 40
t	b, 8, 50
u / v	30
y	g
z	14

Some letters have only a number (e, q, z), some only a letter-symbol (b, m, o, y); e and t have two numbers each.