These two key words are two of the oldest words in Persian language and it’s been more than three thousand years that Iranians have been using these words. Kherad is equivalent of the words Philosophy and Wisdom. One of the most fervent concepts in Shahnameh is used about Kherad (Wisdom). Ferdwosi (the poet) has used the most eloquent praises about Kherad (Wisdom):

Wisdom is a guide, Wisdom is helpful
Wisdom takes your hands in two worlds

Ferdwosi considers the wisdom (Kherad) as God’s Creation. Kherad (Wisdom) is the mixture of reasoning and intuition.
However, the concept of Daad is equally important. In Gahan of Asho Zarathushtra, there is a keyword called Osha that has become Erteh in ancient Persian. These two are defined as the Truth and they mean the law that governs the nature. Ministry of Justice is Esheh Rule or Nature. Therefore, when Ferdwosi mentions the two concepts of Daad and Kherad, in fact he refers to a tradition of two and half thousands years before himself.