The word "base" as used in the passage refers to; loyalty to the family, to the family bond that Ismenia has.
Antigone speaks the words in the given passage to her sister Ismenia. Now, in these words, Antigone questions Ismenia's loyalty and commitment to the family by the use of the word "base" to mean family loyalty.
The reason for use of that word is because their brother was banned from receiving a decent funeral, which prevented his soul from being able to rest in peace. The king then ordered that whoever made a feneral for the brother of Ismenia and Antigona would be condemned to death. However Antígona, in loyalty to her brother, was willing to take that risk and wanted to know if Ismenia had the same loyalty.
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