Why does William Lilly say that

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Why does William Lilly say that,?In a word, some may blame me that I write in the English tongue,yet I trust I have offended on man since I write in my own Language, and to such as speak as I speak, nor do I know that it is forbid unto man to write in his own Language,or is any man bound to read or hear that contents him not??
What happen on the poor Lilly!?

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Very good question, Ming Wei!

I wholeheartedly concur with Curtis's response.

Lilly's 'Christian Astrology' was, when first published in 1647, to the best of my awareness, only the second new printed astrology book to be published initially in English, following the appearance of this one :

G. C. ?A Breef Treatise of Mathematical Phisicke? (1598).

G. C.'s book was an English-language original medical astrology treatise that was appended to the second edition of Claude Dariot's 'A Brief and Easie Introduction to the Astrological Judgement of the Starres', which was a partial* English translation of an originally Latin work. The first edition of the partial* English translation of Dariot had appeared without G. C's added medical astrology treatise in 1583.

Dariot's work was first published in the original Latin as 'Ad Astrorum Judicia Facilis Introductio' in 1557, and then translated into French, long before the first edition of the partial* English translation appeared.

* - The Latin original included also a treatise on electional astrology, including fragments on sickness and critical days. This treatise has never appeared in English translation.

As late as 1645 to 1665, European astrologers' new books were routinely appearing first in Latin, before some of them were translated. For example:

Origanus, David ?Astrologia Naturalis. Sive Tractatus de Effectibus Astrorum Absolutissimus. In quo Omni Astrologiae, ut Vocant, Judiciariae Vanitate? Opus Medicis, Agricolis, Nautis, ac Caeteris Naturalis Actiones?.? Io Baptistae Senii Genuensis, 1645

De Titis, Placido ?Physiomathematica sive coelestis Philosophia Naturalibus Hucusq; desideratis ostensa principiis? with inner title ?Quaestionum Physiomathematicarum Libri Tres? ? Mediolani, A Io. Baptista Maltesta R. Cq; Typographo, undated (but 1650)

Argoli, Andrea ?De Diebus Criticis et Aegrorum Decubitu Libri Duo? Apud Paulum Frambottum Bibliopol.,1652

Argoli, Andrea ?Ptolemaeus Parvus? Sumptibus Iosephi, & Petri Villon, in Via Mercatoria, Lugduni, 1654

De Titis, Placido ?De diebus decretoriis et aegrorum decubitu? Epitome Astrosophica Physicis maxime rationibus, deinde Galeni, Aristot. & Ptolemaei praeceptis contexta? Tomus Primus, Ex Officiana Ioannis Andreae Magrij in Via Nova, 1660

De Titis, Placido ?De Diebus Decretoriis et Morborum Causa Caelesti Ad Iuvandam Praeclaram Artis Medicae Professionem Iuxta Summor? Epitome Astrosophica Physicis maxime rationibus, deinde Galeni, Aristot. & Ptolemaei praeceptis contexta? Tomus Secundus, Ex Officina Ioannis Ghidini, 1665

It would be no exaggeration, therefore, to suggest that Lilly's decision to write first in English was mould-breaking and potentially controversial for its time.

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Cardan generally wrote in Latin in his lifetime, which was much earlier than that of Lilly (16th century, rather than 17th).

Cardan's astrological works appeared in:
1543 (Libelli Duo);
1547 (Libelli Quinque, a major expansion of the above);
1554 (In Cl. Ptolemaei de Astrorum Iudiciis, folio 1st ed.)
1555 (reduced-format octavo 2nd ed. of the above)

The contents of both the Libelli Quinque and In Cl. Ptolemaei de Astrorum Iudiciis were later reprinted in Vol. 5 of the posthumous 'Opera Omnia' over a century later, in 1663.

It is possible that he wrote some works in a vernacular tongue such as Italian; but I'm not aware of them if so. I'd be glad to be enlightened!

English

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There was a big fuss about the Bible being published in English around this time and one historian at least says that was the root cause of the Engish civil war. Maybe that was on Lilly's mind
Matthew Goulding