Obviously, in what follows, I am talking about how I conceptualise God. I'm perfectly aware there are other ways - here I am explaining my-self. Such a question as "How do we know God exists?" can only be answered after a series of counter-questions have been dealt with - so that the question-asker first clarifies his own assumptions about God and the world. Quite likely the asker does not know his own assumptions; or, even worse, assumes that his own assumptions are derived from 'evidence' - which is self-refuting nonsense if you think about it (but people seldom do). We can't know what counts as valid evidence, nor how to interpret it, until after we have assumptions to build-on. Until we know our own assumptions, we don't know whether our idea of evidence is one that we could genuinely endorse. So 'evidence' means nothing-at-all until after we know and endorse the assumptions behind it.
One way to approach this is to focus on the matter of creation; because (by my understanding) God is the creator. So, each person needs to consider: is there is a need to explain creation?
Do we, on the one hand, assume we live in a world with genuine, objective, purpose and meaning? Or do we believe that reality is simply some mixture of determinism (things deterministically causing other things) and randomness (things just happening, disconnected from causes)? Do we believe that creation is intentional, or that there is no creation and things Just Are.
And by 'do we assume' I mean to ask whether that specific person actually makes this assumption, for himself, or not; because this is metaphysics, which is a matter of assumptions and not of 'proof' or 'evidence'. So I am asking about your primary intuitions, your bottom-line beliefs about the nature of your life in this world and the nature of yourself and the world: do you (as a matter of actuality) assume meaning, or not?
Because only if you assume that this world has meaning can you know that God exists.
If you assume no meaning or purpose - you have already ruled-out the existence of God, and need not think about it any more.
Indeed, you have already (implicitly) assumed that your thinking is just a part of the reality of determined causes and/or randomness; so you are assuming that your thinking does not signify anything about reality: It Just Happens.
You need to think - therefore - about whether you really and truly assume there is no purpose and meaning to anything; because if you do assume this, then why are you talking about things like God? In fact, why are you trying to exlain anything to anybody? You have already decided it means nothing.
If things do have purpose and meaning, they are created; and if they are created then there is 'a creator' - but you have not yet decided what a creator may be.
The next question is whether the creator is a person or not.
This is again a matter of fact; so how can one find out such facts?
Again, there is no possibility of the question being decided by 'evidence'; so it must be a matter of intuitive assumption. You need to examine your own bottom line assumptions.
When you think deeply and clearly, do you know a personal creator? Or do you assume a creator that is impersonal - a force, tendency, some abstract principle?
At bottom: is reality (as you know it) personal, or not?
If you regard creation as personal; you are a theist - that is, you know God exists: you 'believe in God'; but you then you may feel the need to consider the nature this God.
(One could say, "I know there is a God who is creator", but I have no interest beyond that. Either you have the desire to know the nature of this God, or you don't.)
How to discover the nature of God? Is this even possible? More assumptions...
Well, you have by now clarified that there is a personal creator; and you can then clarify whether this creator has a relationship with us, or not; whether God is indifferent to you, or interested and concerned with you?
Either you will have a positive knowledge of God's personal relationship with you, or this will be lacking. (One cannot know that God is indifferent - one can only know that one feels no interest from God).
Again, this is an intuitive kind of knowledge. Since God is creator, he is present in all of creation (including myself, to at least some extent) - so if God does have a relationship with me personally, then I can know it. A God that has a personal relationship with me, can make this known to me (if he wishes - and if I acknowledge it).
And then - finally - one will know if the personal creator God loves us, whether he loves me personally.
If he does love me, then I can know this by knowing God in-creation (in everything created around me), and by knowing God in myself - insofar as I am created.
If, therefore, I know God the creator, who loves me, exists; and I know his nature; then I can see evidence for this all around and within me.
But if God exists but does not love me, then he may not want me to know about him; he may not care whether I know his reality - his existence may be hidden.
So it seems that the question "How do we know God exists?" can be answered; but that it can be answered only after assumptions have been clarified; and it can only be answered for some (not all) assumptions concerning the nature of reality and God, and on the basis of some of the possible assumptions concerning the nature of God.
For the assumptions that I personally have about creation, God and the nature of God; I can know that God exists. But that need not apply to you. Many modern people have already, implicitly, assumed God as creator does not exists: and it is then their assumptions that prevent them from knowing.
Before accepting any conclusion, we need to discover and clarify our own probably unconscious and unknown assumptions; because once these are made clear and explicit, it may turn out that we do not, after all, regard our unconscious assumptions as true.
Such is the value, the necessity, of thinking about metaphysics.
