Chapter XV.--The Objection to Join the Church on Account of the Diversity of Heresies Answered.
Since it comes next to reply to the objections alleged against us by Greeks and Jews; and since, in some of the questions previously discussed, the sects also who adhere to other teaching give their help, it will be well first to clear away the obstacles before us, and then, prepared thus for the solution of the difficulties, to advance to the succeeding Miscellany.
First, then, they make this objection to us, saying, that they ought not to believe on account of the discord of the sects. For the truth is warped when some teach one set of dogmas, others another.
To whom we say, that among you who are Jews, and among the most famous of the philosophers among the Greeks, very many sects have sprung up. And yet you do not say that one ought to hesitate to philosophize or Judaize, because of the want of agreement of the sects among you between themselves. And then, that heresies should be sown among the truth, as "tares among the wheat," was foretold by the Lord; and what was predicted to take place could not but happen.  And the cause of this is, that everything that is fair is followed by a foul blot. If one, then, violate his engagements, and go aside from the confession which he makes before us, are we not to stick to the truth because he has belied his profession? But as the good man must not prove false or fail to ratify what he has promised, although others violate their engagements; so also are we bound in no way to transgress the canon of the Church.  And especially do we keep our profession in the most important points, while they traverse it.
Those, then, are to be believed, who hold firmly to the truth. And we may broadly make use of this reply, and say to them, that physicians holding opposite opinions according to their own schools, yet equally in point of fact treat patients. Does one, then, who is ill in body and needing treatment, not have recourse to a physician, on account of the different schools in medicine? No more, then, may he who in soul is sick and full of idols, make a pretext of the heresies, in reference to the recovery of health and conversion to God.
Further, it is said that it is on account of "those that are approved that heresies exist."  [The apostle] calls "approved," either those who in reaching faith apply to the teaching of the Lord with some discrimination (as those are called skilful  money-changers, who distinguish the spurious coin from the genuine by the false stamp), or those who have already become approved both in life and knowledge.
For this reason, then, we require greater attention and consideration in order to investigate how precisely we ought to live, and what is the true piety. For it is plain that, from the very reason that truth is difficult and arduous of attainment, questions arise from which spring the heresies, savouring of self-love and vanity, of those who have not learned or apprehended truly, but only caught up a mere conceit of knowledge. With the greater care, therefore, are we to examine the real truth, which alone has for its object the true God. And the toil is followed by sweet discovery and reminiscence.
On account of the heresies, therefore, the toil of discovery must be undertaken; but we must not at all abandon [the truth]. For, on fruit being set before us, some real and ripe, and some made of wax, as like the real as possible, we are not to abstain from both on account of the resemblance. But by the exercise of the apprehension of contemplation, and by reasoning of the most decisive character, we must distinguish the true from the seeming.
And as, while there is one royal highway, there are many others, some leading to a precipice, some to a rushing river or to a deep sea, no one will shrink from travelling by reason of the diversity, but will make use of the safe, and royal, and frequented way; so, though some say this, some that, concerning the truth, we must not abandon it; but must seek out the most accurate knowledge respecting it. Since also among garden-grown vegetables weeds also spring up, are the husbandmen, then, to desist from gardening?
Having then from nature abundant means for examining the statements made, we ought to discover the sequence of the truth. Wherefore also we are rightly condemned, if we do not assent to what we ought to obey, and do not distinguish what is hostile, and unseemly, and unnatural, and false, from what is true, consistent, and seemly, and according to nature. And these means must be employed in order to attain to the knowledge of the real truth.
This pretext is then, in the case of the Greeks, futile; for those who are willing may find the truth. But in the case of those who adduce unreasonable excuses, their condemnation is unanswerable. For whether do they deny or admit that there is such a thing as demonstration? I am of opinion that all will make the admission, except those who take away the senses. There being demonstration, then, it is necessary to condescend to questions, and to ascertain by way of demonstration by the Scriptures themselves how the heresies failed, and how in the truth alone and in the ancient Church is both the exactest knowledge, and the truly best set of principles (airesis). 
Now, of those who diverge from the truth, some attempt to deceive themselves alone, and some also their neighbours. Those, then, who are called (doxosophoi) wise in their own opinions, who think that they have found the truth, but have no true demonstration, deceive themselves in thinking that they have reached a resting place. And of whom there is no inconsiderable multitude, who avoid investigations for fear of refutations, and shun instructions for fear of condemnation. But those who deceive those who seek access to them are very astute; who, aware that they know nothing, yet darken the truth with plausible arguments.
But, in my opinion, the nature of plausible arguments is of one character, and that of true arguments of another. And we know that it is necessary that the appellation of the heresies should be expressed in contradistinction to the truth; from which the Sophists, drawing certain things for the destruction of men, and burying them in human arts invented by themselves, glory rather in being at the head of a School than presiding over the Church.