# Choosing axiom schemes for a logical theory

In a Hilbert system, there are many ways that we can choose axiom schemes. My question is:

1- How do we know that we have defined enough schemes? What would happen if I remove a scheme from the list?

2- How do we decide on the form of these schemes?

3- How can we determine that a particular choice of axioms results in a consistent theory?

Please also let me know if you know a source that discusses such issues.