def _get_states(rev, act):
    """Determines the initial state and the final state based on boolean inputs

    Parameters
    ----------
        rev : bool
            True if the reaction is in the reverse direction.
        act : bool
            True if the transition state is the final state.
    Returns
    -------
        initial_state : str
            Initial state of the reaction. Either 'reactants', 'products' or
            'transition state'
        final_state : str
            Final state of the reaction. Either 'reactants', 'products' or
            'transition state'
    """
    if rev:
        initial_state = 'products'
        final_state = 'reactants'
    else:
        initial_state = 'reactants'
        final_state = 'products'
    # Overwrites the final state if necessary
    if act:
        final_state = 'transition state'
    return initial_state, final_state