Chapter III.--Justin narrates the manner of his conversion.
"And while I was thus disposed, when I wished at one period to be filled with great quietness, and to shun the path of men, I used to go into a certain field not far from the sea. And when I was near that spot one day, which having reached I purposed to be by myself, a certain old man, by no means contemptible in appearance, exhibiting meek and venerable manners, followed me at a little distance. And when I turned round to him, having halted, I fixed my eyes rather keenly on him.
"And he said, Do you know me?'
"I replied in the negative.
" Why, then,' said he to me, do you so look at me?'
" I am astonished,' I said, because you have chanced to be in my company in the same place; for I had not expected to see any man here.'
"And he says to me, I am concerned about some of my household. These are gone away from me; and therefore have I come to make personal search for them, if, perhaps, they shall make their appearance somewhere. But why are you here?' said he to me.
" I delight,' said I, in such walks, where my attention is not distracted, for converse with myself is uninterrupted; and such places are most fit for philology.' 
" Are you, then, a philologian,'  said he, but no lover of deeds or of truth? and do you not aim at being a practical man so much as being a sophist?'
" What greater work,' said I, could one accomplish than this, to show the reason which governs all, and having laid hold of it, and being mounted upon it, to look down on the errors of others, and their pursuits? But without philosophy and right reason, prudence would not be present to any man. Wherefore it is necessary for every man to philosophize, and to esteem this the greatest and most honourable work; but other things only of second-rate or third-rate importance, though, indeed, if they be made to depend on philosophy, they are of moderate value, and worthy of acceptance; but deprived of it, and not accompanying it, they are vulgar and coarse to those who pursue them.'
" Does philosophy, then, make happiness?' said he, interrupting.
" Assuredly,' I said, and it alone.'
" What, then, is philosophy?' he says; and what is happiness? Pray tell me, unless something hinders you from saying.'
" Philosophy, then,' said I, is the knowledge of that which really exists, and a clear perception of the truth; and happiness is the reward of such knowledge and wisdom.'
" But what do you call God?' said he.
" That which always maintains the same nature, and in the same manner, and is the cause of all other things --that, indeed, is God.' So I answered him; and he listened to me with pleasure, and thus again interrogated me:--
" Is not knowledge a term common to different matters? For in arts of all kinds, he who knows any one of them is called a skilful man in the art of generalship, or of ruling, or of healing equally. But in divine and human affairs it is not so. Is there a knowledge which affords understanding of human and divine things, and then a thorough acquaintance with the divinity and the righteousness of them?'
" Assuredly,' I replied.
" What, then? Is it in the same way we know man and God, as we know music, and arithmetic, and astronomy, or any other similar branch?'
" By no means,' I replied.
" You have not answered me correctly, then,' he said; for some [branches of knowledge] come to us by learning, or by some employment, while of others we have knowledge by sight. Now, if one were to tell you that there exists in India an animal with a nature unlike all others, but of such and such a kind, multiform and various, you would not know it before you saw it; but neither would you be competent to give any account of it, unless you should hear from one who had seen it.'
" Certainly not,' I said.
" How then,' he said, should the philosophers judge correctly about God, or speak any truth, when they have no knowledge of Him, having neither seen Him at any time, nor heard Him?'
" But, father,' said I, the Deity cannot be seen merely by the eyes, as other living beings can, but is discernible to the mind alone, as Plato says; and I believe him.'