This Nirgun-Sargun duality can be recognised as nothing except a contradiction in terms.
We recommend those unfamiliar with the Law of non-Contradiction to read the following article refuting those who ignorantly claim this law not to be self-evident or a priori, or those who assert this law to be man-invented, thus, deducing that God cannot be limited or restricted to these alleged man-invented laws:
In the Qur'an Allaah establishes that something and its opposite cannot both be accepted as true at the same time:
"And such is your Lord in truth. Then what is there after Truth except falsehood. How have they then turned away?" (Qur'an 10:32)
If something is accepted as true, anything in opposition to that is rendered false.
Hence, from the universal Law of non-Contradiction: (P and not-P) is false, if:
Nirgun (unattributed) is taken to be proposition P, then Sargun (attributed), its opposite and negation, is not-P.
Since the Sikhi concept of God affirms Him to be both Nirgun and Sargun at the same time and in the same respect, we must conclude that (P and not-P) is false, a contradiction and must be rejected by the rational mind.