Saajan Sandhu contacted Islam-Sikhism with an email titled: People who live In in Glass House Dont throw stones at others [sic]. He assured us he would refute all our articles one by one. We welcomed his rebuttals by assuring him that these would, subject to the rules of debate, be published in full.
This is an extract reply from a very learned sikh brother which I think is sufficient to answer your question.
Sargun and Nirgun aspects of eternal reality would appear contradictory to those who base their judgement on their own subjective human frame of reference.
This “very learned” Sikh’s very first assertion that valid logical conclusions can be reached through subjective analysis is self-defeating. It may be that one’s epistemology is subjective, but the laws of bi-valued logic are the same for all epistemological models, systems and situations. Hence, the determination of truth is and will always be bound by these logical absolutes.
We wish to ask whether the assertion that the “Sargun and Nirgun aspects of eternal reality would appear contradictory to those who base their judgement on their own subjective human frame of reference” is true, and we ask this “very learned” Sikh to prove it is true subjectively.
By definition, Sargun is that which can be perceived by human senses. That is, the material universe, gods, incranations etc. The duality is not in the eternal reality appearing as a contradiction to some but in the ability and inability to be able or not able to perceive through human senses.
Subject to correctly interpreting this vague paragraph, we have concluded that the Nirgun-Sargun “duality” is a contradiction based not upon our perception of its reality, but firstly its etymological structure, i.e. the suffix ‘gun’ means ‘attributes’, ‘sar’ means ‘with (all)’ and ‘nir’ means ‘none’. God is, thus, described as Sargun – a deity with attributes (attributed), but also Nirgun – an attributeless deity (unattributed), which of course is a contradiction in terms. The so-called subjective reality of this duality, however, has no bearing on the fact that etymologically the Nirgun-Sargun concept is a contradiction. But, we have no hesitation in extending this to say that conceptually speaking, this model is also contradictory.
Using a scientific analogy from cosmology one can say that most of the matter can be seen or perceived but the black holes cannot be directly seen hence one could say that black holes as matter and the rest of the matter are two contradictory things in the sense that if both are matter why one can be seen and the other not if the classical definition of matter is that it can be perceived through senses.
It is surprising to see a Sikh forced into striking vacuous analogies in an attempt at vindicating this errant and irrational concept of God.
The analogy is false because if what is meant by ‘perceived’ is direct awareness through the senses, especially sight or hearing, then this is not an exhaustive definition since to perceive also means to achieve understanding or apprehension of something.
Hence, some black holes may not be directly seen, but one could perceive of their existence through indirect analysis. However, this learned Sikh has been hasty in presuming that black holes cannot be seen directly when in fact observational evidence for such galactic phenomena do exist with the discovery of the NGC4261 galaxy and, of course, the famous M87 galaxy. 
On the same lines, It is due to the human shortcoming that the Nirgun cannot be perceived and Sargun can be.
As we said before, our conclusion that the Nirgun-Sargun concept is contradictory is not based upon our perception of its reality, but its etymological structure. The subjective reality of this concept has no bearing on the fact that etymologically it is contradictory.
Before applying any logic to such situations it is important that we must look at the presumptions we make about the objects or concepts we discuss.
Guru ji has given several variations on the Nirgun God as well. He is Ekankar (with attributes like the number one, Ek Ank, as in numbers theory, being present in all numbers as a factor but being separate and unique from all other numbers) or as Oankar (as a sound giving order to create “Oankar Brahma Utpat” Oankar sound created god Brahma to create, “Oankar Keea Jin Chit” the Oankar sound form that created conciousness.
Above all God is Nirankar (Nir + Ank + Kar) Not even like an Ank or number. Meaning Nirankar is a negative description of Ekankar saying that God is, may be even other than Ekankar which is only a mathematical attribute of God.
This is where the Sikhs’ problem is further compounded because etymologically, the Nirgun god was both Ekankar (Ek (1) Ank; singularity) and at the same time the negation of Ekankar, that is, Nirankar (Nir (none) Ank), what can be translated as formless. Then prior to creation, the claim is that God willed to create through the sound Oankar. But you fail to explain these definitions in light of the post-creationary manifestation of God – Sargun, and this is the crux of the problem.
Following Oankar, God manifested as Sargun, but the damning factor is that He still remained Nirgun. Hence, following Oankar, He is both Nirgun and Sargun at the same time.
Hence, as Nirgun, while He is both Nirankar and Ekankar – the formless and attributeless 1, He is also, at the same time, the opposite in the form of Sargun, or the one who is attributed and formed. Hence, in relation to the law of non-contradiction, no matter which way you look at the theology-proper of Sikhism, it is a classic contradiction in terms.
Furthermore, Gurbani tells us that God is not just Sargun, or Nirgun, or Ekankar, but is Akath that can not be described, Human beings are incapable of describing it.
We agree. It is God who describes Himself. However, if it is said that God is ineffable, then He should remain silent concerning His Divine Self. Yet, SGGS is full of God’s descriptions, which Sikhs hold to be revelation/ inspiration from Him; and since it is He who has described Himself, these descriptions are subject to rational scrutinisation.
Are you or your Islam able to describe God? If so ….
Allah has described His Self just as Sikhs claim Waheguru has. If, in this regard, you find fault with Islam but not with Sikhism then you are being inconsistent.
Next you have attacked Guru Dev Ji. I will reply you on that too.
We look forward to it, God willing.