Summum bonum is a Latin expression meaning "the highest good", which was introduced by Cicero, to correspond to the Idea of the Good in Ancient Greek philosophy.

Ususally, a if a classic Latin term in the text , you just use "Summum bonum" and leave as it is.

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Note added at 14 mins (2015-10-08 20:34:50 GMT)
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Ethics - Page 146
https://books.google.hu/books?isbn=0521388325 -
Stephen Everson - 1998 - ‎Philosophy
Pleasure was introduced at the outset, back in the Cradle Argument, as the ... The phrase summum bonum occurs literally hundreds of times in Cicero's ...

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Note added at 16 mins (2015-10-08 20:36:23 GMT)
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you may say also "the supreme good"


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Note added at 17 mins (2015-10-08 20:37:15 GMT)
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CICERO, De Finibus Bonorum et Malorum
www.loebclassics.com/...cicero.../pb_LCL040.217.xml
Quaerendum est enim ubi sit illud summum bonum quod reperire volumus,

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Note added at 20 mins (2015-10-08 20:40:34 GMT)
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Summum bonum in English
highest good, greatest good (Latin)

Summum bonum in Russian
величайшее благо

Summum bonum in Italian
il bene maggiore, sommo bene (lat.)

Summum bonum in German
höchste Gut (Latein)

Summum bonum in Hebrew
(לטינית), הטוב הנעלה, המוסר העליון

Summum bonum in English / The highest good. All values must be defined in terms of this ultimate value. All aims must lead to this single, ultimate aim

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Note added at 21 mins (2015-10-08 20:41:49 GMT)
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I checked in 4 langiages I speak, they are correct (EN, DE, IT, RUS) I hope I found it for you

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Note added at 2 hrs (2015-10-08 22:59:51 GMT)
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see here

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Note added at 4 days (2015-10-13 06:05:20 GMT) Post-grading
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Thank you very much.