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In page Semiotics:

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It would not be until Augustine of Hippo[4] that the nature of the sign would be considered within a conventional system. Augustine introduced a thematic proposal for uniting the two under the notion of 'sign' (signum) as transcending the nature–culture divide and identifying symbols as no more than a species (or sub-species) of signum.[5] A monograph study on this question was done by Manetti (1987).[6][7] These theories have had a lasting effect in Western philosophy, especially through scholastic philosophy.[citation needed]