In Buddhism we speak of three types of phenomena: First, there are evident phenomena that are perceived directly.
Second, there are slightly hidden phenomena, which are not accessible to immediate perception. There are differences of opinion on this even within Buddhist philosophy. Generally speaking, we think this second type of phenomena can be known indirectly by inference.
One example of something known by inference is that anything arising in dependence upon causes and conditions is itself subject to disintegration and momentary change. This momentary change is not immediately evident to your senses. You can look at something with your eyes, and it does not appear to be changing right now, but by inference you can know that it is momentarily changing. This is an example of the second category of phenomena.
Third, there are very concealed phenomena, which cannot be known by either of the two preceding methods. They can be known only by relying upon testimony of someone such as the Buddha
