It seems to me that you have a choice when discussing the use of words and semantics. You can get overly ponderous in the denotative meanings, or you can arbitrarily grasp for connotative meaning. Even though I hate resorting to dictionary definitions, I don't think I can avoid it in this case. Merriam-Webster defines the noun "know" in several ways:
- to perceive directly : have direct cognition of
- to have understanding of (importance of knowing oneself)
- to recognize the nature of : discern
- to recognize as being the same as something previously known
- to be acquainted or familiar with
- to have experience of
- to be aware of the truth or factuality of : be convinced or certain of
- to have a practical understanding of (knows how to write)
It seems those who claim that no one can really know things of the Spirit are looking at definitions 1) and maybe 7). They disingenuously claim that you cannot know (or most people don't know) because any claim to perceive something directly is negated by another's claim to perceive the opposite, and that you cannot be aware of the factuality of a spiritual truth for the same reason - that another may claim an opposite factuality.
This argument is entirely erroneous and fails to understand the nature of truth. If Jane is blue/yellow colorblind and sees the sky as a flat shade of blue-green, she can testify that she knows the sky is flat. If Sally can see all the shades of blue, from pale to rich, in the sky, she can testify to the gradation of color. One person's testimony does not negate another's. Mary has a doctorate in spectrophotometry. She can not only explain that there is a perceptual gradient, but also explain how it is completely based on perception and not a physical change in the makeup of the atmosphere. She can testify to a deeper truth about the sky's color. That still does not negate or invalidate the testimonies of Jane and Sally. They are still valid testimonies. Furthermore, even Mary, with all her knowledge and qualifications, can not necessarily explain the base nature of light. There is always more truth to discover.
At the risk of getting overly philosophical, the interesting thing is that intangible truths can be drawn from all three testimonies. Each of them have something to contribute to the understanding of Truth. That is why Christ taught (and teaches) at the level His disciples could understand. He was able to take truths they all knew—such as the size of a mustard seed—and draw out still greater lengths of actual knowledge. Their previous knowledge was not invalidated any more than a roof on a house invalidates the basement footings.
Most cannot understand how seemingly diametrically opposed testimonies can both be true without resorting to relativistic theory—that different things are true to different people. A better way to say it is that different people see things differently. It is a subtle parsing of meaning, but picture it as though Truth was a plant. Many would like to say that there is a different plant for each person. Rather say that there is one great plant that we all see a little differently. Once we have gained all knowledge and all understanding, we will realize that it is the same plant. We all have something to gain by sharing another's understanding.
Be careful if you feel the urge to put "know" into quotes. Just because you do not know something, doesn't mean another person does not. You are revealing far more of your own ignorance than of your superior understanding of truth.