I recently came upon an intriguing debate about the existence of Glauber states in quantum optics. In 1997 Klaus Mølmer published a paper with the title "Optical coherence: a convenient fiction" that challenged the textbook wisdom that the laser field above threshold is a Glauber coherent state. His reasoning is essentially that the state of the electromagnetic field should be thought of as the reduced density operator after tracing out the atoms in the gain medium. This gives rise to a density operator that is diagonal in the number of photons basis with identical diagonal elements as the Glauber state, but without off-diagonal coherences. The notion of such coherences plays an important role in how one usually understands experiments like homodyne detection, or in different contexts BEC interference experiments or BCS ground states. This 1997 paper ignited (or re-ignited) a lively debate that led to countless publications, nicely summarised in a paper entitled "Dialogue Concerning Two Views on Quantum Coherence: Factist or Fictionist" by S. Bartlett, T. Rudolph and R. Spekkens. Their conclusion is that neither side wins the debate, both viewpoints are possible and internally consistent. One key ingredient is that the number diagonal mixed state is equal to the incoherent superposition of Glauber states when averaging over the unknown phase of the Glauber state. Going through the dialogue between the "factist" and the "fictionist" is fun (disclaimer: for physicists) and points to interesting and fundamental problems.