Atheism (lack of belief that God exists) depends on definition of (attributes assigned to) God. Deism & ‘Randomly behaving God’ are not falsifiable. But one of the prerequisites to admit any proposition as possibly true is, it has to be falsifiable. For instance, if I say, “there exists a force between 2 balls such that it is directly proportional to the product of their masses, & inversely proportional to the square of distance between them”, & call it theory of ‘mystical gravity’, then such a statement is NOT falsifiable as I have not specified the direction of force. Such a statement cannot be disproved by actual or thought experiments. If we conduct an experiment with Newton’s original theory as hypothesis, then it is falsifiable. How? If you place two balls in a frictionless environment, the (UNIQUE) prediction is that they will be attracted with predicted force & will accelarate (with predicted value) TOWARDS EACH OTHER for ALL combinations of mass & distance. If any of these do NOT occur (say, balls move away from each other), then Newton’s theory would be proved wrong. But the mystical theory cannot be falsified (as it gives MULTIPLE predictions), because irrespective of how the two balls move in each others’ presence, I can always say, “see, force is predicted, but we do not know which component of force is acting in which direction”! Thus, one would have to acknowledge existence of a (directionless) ‘mystical force of gravitation’ independent of how balls behave.
Analogy from mathematics: any REAL function must yield a unique value ‘y’ (dependent variable) for any given value of ‘x’ (independent variable). Why? As we want to derive a “law” that would be able to PREDICT the outcome (‘y’) each time we are given a defined situation ‘x’ (e.g., distance between two particles of constant mass). Now, most of the definitions of God are such that they do not give a unique result (“God’s ways cannot be known” or “God only knows”) for any given situation. So, any reasoning based on such a God’s involvement would be like an unreal function.
Most of the concepts of God are like
mystical theory of gravitation. You can claim God exists (like mystical gravity), but cannot predict how God will behave (undefined direction of force).