Gratitude (n.) is the mother of the virtues.
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Gratitude (n.) is not only the greatest of virtues, but the parent of all the others.
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Gratitude (n.) and generosity are the bonds of mutual harmony.
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Gratitude (n.) should be like fertile fields, which bring forth far more than they received.
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Gratitude (n.) is the one debt that is held by being paid: he who has money has not repaid it; he who has repaid it has it not; but he who has returned kindness has it, and he who has it has returned it.