Debating an atheist, like debating a solipsist, is an exercise in futility. One cannot reason a man out of what he was not reasoned into.
The solipsist reasons that all true knowledge is empirical, that is, from the sense impressions. No sense impression confirms minds or spirits exist in other men, since they all may be cleverly constructed waxwork automatons. Therefore belief in minds behind the acts and words of other men is not true knowledge. Other men do not exist. Only me.
Now, the solipsist argument can be written in the form of a syllogism. Major Premise: all true knowledge is empirical. Minor premise: we have no empirical knowledge other men exist. Conclusion: other men do not exist.
But, nonetheless, it is not a rational argument. Solipsism is a sociopathic psychosis. Or it would be if anyone who argued this way actually believed it.
And, of course, the major premise is false.
All true knowledge is not empirical. If it were, then this statement "all true knowledge is empirical" would not be true knowledge, as the statement itself cannot be confirmed by a sense impression (for "true knowledge" has neither extension, duration, hue, sound, nor odor).
And the minor premise is false. We do have empirical knowledge of the acts and words of other men, and these the acts and words of the friends and enemies around us, lovers and rivals, cannot be explained as merely cleverly constructed waxwork automatons: too much daily behavior is not mere clockwork repetition. Men can pass the Turing Test.
Moreover, the conclusion does not follow from the axiom.
Even if Robinson Crusoe, when they are beyond the range of his senses, has no true knowledge of other men, this does not mean he can conclude only he exists.
Absence of evidence is not evidence of absence.
His own existence, by itself, demonstrates other men at least at one time existed: his mother and father, if no one else, and whoever devised the English language in which he writes his journal. The evidence still within the range of his senses, namely, his own acts and words, and the artifacts saved from the shipwreck built by rational intelligence, does not allow for reasonable doubt.
Or, again, a worldwide plague or attack by jaguars might have wiped out all of mankind in the months since the shipwreck. He does not have certain knowledge this did not happen. But it is not a reasonable doubt.
And, in any case, even if you did not know that other men existed with apodictic certainty, that is, proof beyond unreasonable doubt, you know it with proof beyond all reasonable doubt. To ask for proof beyond unreasonable doubt is unreasonable.
The atheist argues likewise.
He asks for empirical proof for God, when the existence of God is a metaphysical or theological question, where the empirical proof neither confirms nor denies. As if Hamlet were to demand Shakespeare meet him in a fencing match: but Shakespeare, unlike Laertes, is not a character in the play, but the playwright.
On the other hand, the Christian God added an autobiographical character in the person of Christ, whose historical reality cannot be doubted except by the kind of crackpot who doubts that Caesar existed, or Constantine, or Charlemagne, or Charles II.
Likewise again, even as we can judge from the acts and words of a man whether he is alive or a waxworks, we can judge from the acts and words of Christendom whether a holy spirit moves and lives in them. This may seem a doubtful test at first, since so many false prophets and charlatans exist, but please consider:
Atheists routinely accuse Christendom of various crimes and shortcomings, such as supporting slavery, oppressing women, waging holy war, or hindering the progress of science.
Note that the Christian is never accused of something all mankind has not always done since the dawn of time. He is only accused of those things he himself and no one else has opposed or mitigated or abolished.
No one ever spoke a word against slavery until Christians opposed and abolished it. Wherever Christianity is waning in the world, slavery is returning.
No one ever held that women were equal in the eyes of God until Christians promoted the idea. There were, yes, queens in pagan days and pagan lands, but only Christians forbade divorce, enforced monogamy, required the consent of the bride to wed, allowed women to own property, to stand for public office, and to vote. Observe the Mohammedan world for contrast, where women are chattel, or the Communist, where all folk are.
There is no crusade of Christendom as deadly or unjustified as the jihads of the Mohammedan or the genocides of the Socialists, which were, by any rational definition, holy wars.
As for the progress of science, this argument, or, more accurately, this talking point of absurd propaganda could not possibly be less convincing. It merits an award for its insolence.
The scientific method cannot be produced and cannot exist outside of the Christian worldview. Confucius dismisses inquiry into the origin of things as impossible. Aristotle is an armchair philosopher. Buddha regards the world as an illusion. Mohammed holds all things to be directly willed by God, without secondary causes to examine.
Science can indeed be taught and practiced outside Christendom, but only be folk who copy the metaphysical assumptions of the Christian worldview. Even then, the secular nations of Nazi Germany, Soviet Russia, produce junk science, race science, Mengele and Lysenko. Post Christian America produces Climate Science and Critical Gender Theory, where popular "scientists" assert that gender is a fluid spectrum, and that plagues do not spread during race riots.
Christendom abolished slavery, equalized the sexes, liberated mankind, abolished routine sexual perversions, invented and promoted the natural sciences, and meanwhile invented modern medicine, musical notation, perspectival drawing, the pointed arch, the stirrup, the jib sail, the clipper ship, the common law, trial by jury, the flying machine and the moonshot. None of this was done by waxwork mannikins.
What empirical proof there is, in the form of the witness of history and the physical evidence of miracles, the atheist does not examine.
I myself have talked to crackpots claiming the Miracle of the Dancing Sun at Fatima was caused by all the thousands of eyewitnesses growing dazed because they stared upward at the sun. A flat earther has a more convincing argument.
The Shroud of Turin, the Mantle of Our Lady of Guadalupe, the miracle healings at Lourdes, the images in the rock at Our Lady of Las Lajas, and the countless Eucharistic miracles are simply never examined, or are dismissed with feeble ad hoc explanations.
Like Crusoe, the atheist is free to examine himself, his moral sense, his rational faculties, his history, the beauty and order of nature, and come to the same reasonable conclusion all men of all history and prehistory have reached: these things did not arise by mischance, without meaning, without point.
If to conclude that cause and effect exists is a proper metaphysical presumption for modern science, then to conclude that an uncaused first cause exists is likewise.
If one looks at one's fellow man, and sees only waxwork automatons, one is a sociopath. If one looks at nature, and sees only automatons that emerged from nothing toward no purpose, one is an atheist.
But, for the atheist, nature is all that there is, including his own mind, his own sense of right and wrong, good and evil, true and false, reasonable and unreasonable. It is by the use (or otherwise) of these faculties that he comes to the conclusion that atheism is true and God is false.
But if his own mind is merely an accident of nature, and if nature is blind and pointless, then his own mind is blind and pointless: merely a clockwork of marching atoms and firing neurons, signifying nothing.
His so-called reasoning by which he reached his conclusion, either about atheism or about any topic, is merely the blind repetition of meaningless matter in motion. It is not a conclusion, not a truth. It is a row of brain-atom dominoes toppling, each one falling for no other reason than the one before toppled.
Atheism logically necessitates man has no soul, and that his mind is an illusion caused by matter in motion. In which case, if the mind is material, merely the clatter of moving matter, it is not, in any proper sense of the word, a mind.
A solipsist is a lunatic who believes he alone exists. An atheist is a lunatic who believes he does not exist.
The mere act of making an argument in favor of solipsism, if you are talking to another man about it, proves that the minds of other men exist. Likewise, the mere act of making an argument in favor of atheism, if one appeals to standards of knowledge, of logic, or of right and wrong, proves something beyond nature exists.