Instrumental faith and personal faith
Augustine’s notion of faith can be divided into two main groups. In the first group, we find interpretations of faith consistent with earlier conceptions; nevertheless, even these conceptions offer at some points characteristic novelties. In the second group, we find his own unique and momentous notion of faith, which could be said to have created a new epoch in the history of faith. The conceptions which belong to the first group are arranged around the central point of faith instrumental to knowledge. Instrumental faith is often seen by Augustine as permeating the whole range of mental activities, inasmuch as there are various kinds of credible things: those always believed but never understood; those understood as soon as believed; and those things first believed and afterwards understood. History and the temporal things of humanity belong to the first group; mathematical and logical axioms and rules belong to the second group; and ‘things divine’ belong to the third group. It is interesting to see how Augustine subsumes various mental activities under the rubric of ‘faith’, for he seems to think that faith equally has a probability character (first group), an axiomatic nature (second group) and a theological feature (third group). Naturally, these cases deal with different mental activities, but for Augustine it is more important to emphasize that ‘believing’ permeates and naturally present in the human mind.
Instrumental faith has a morally purifying function. Augustine refers to Acts 15.9 (‘purifying their hearts by faith’) in order to emphasize the role of faith in preparing higher states of mystical consciousness, knowledge and vision. Purity of heart is the precondition of the knowledge of God, ‘faith is understanding’s step and understanding is faith’s reward’.   ‘Seek not to understand that you may believe, but believe that you may understand’.10 11 ‘Believe that you may understand’ is the key expression Augustine unremittingly emphasizes, thereby making faith the instrument of knowledge of God.
On the other hand, instrumental faith is underpinned by authority and reason. This seems to be circular, since Augustine often declares faith to be the beginning of knowledge. However, faith is motivated by love, authority and everyday reason alike; faith purifies the heart and opens the ‘eyes of reason’, which leads us to a higher order of faith. This later opens the way to the knowledge of the mysteries of God, a knowledge supernatural and ineffable at the same time. ‘For there are some things which we do not believe unless we understand them, and there are other things which we do not understand unless we believe them’.11 In this mutual relationship, faith is often depicted as intellectual, as ‘an assent to the truth of what is said’. Yet Augustine never really sees faith as purely intellectual. His central expressions, such as ‘assent’ or ‘will’, always involve ‘the heart’, ‘love’ and the ‘interior eyes’. These expressions help us to determine the other kind of faith in Augustine which we may term faith ‘sui generis’ or personal faith.
With respect to personal faith, an important reference for Augustine is the verse from Isaiah: ‘If ye will not believe, surely ye shall not be established’ (7.9). Characteristically, Augustine - following the Greek and Latin translations of his time - understands this verse as ‘Unless you believe, you shall not understand’. In his interpretation, this faith is not merely initial or instrumental. Faith here is a faith of absolute magnitude which permeates the whole range of human activities and goes even deeper into the ‘heart’; it grasps the core of personhood. Augustine’s unparalleled novelty is his clearly formulated notion of the necessity of a personal faith. Certainly, many of his formulas reflect the traditional aspects of instrumental faith, but at crucial points the new dimension of sui generis faith comes to the fore.
In spite of the eloquent and often lecturing style of the professional rhetorician, Augustine seems to be hesitating about the very nature of faith. Even in the circle of instrumental faith, he does not clearly distinguish between rational, emotional, purifying and mystical faith. He does, however, have to distinguish the personal kind of faith from all other kinds.