What is manifest is known by valid perception.
What is hidden is known by valid inference.
What is extremely hidden is known by valid testimony.
In the presence of fire, seeing the flames and feeling the heat constitutes valid perception.
At a distance from the fire, seeing the smoke and understanding that ‘where there is smoke, there is fire’ constitutes a valid inference.
At a further distance from the fire (in time or space), hearing from a reliable witness about the fire constitutes a valid testimony.