If a reasonable sceptic says that such things do not exist, he can only mean to say that they do not exist relatively to his knowledge ; because, to deny the possibility of the existence of anything of which we know nothing would imply that we imagined ourselves to be in possession of all the knowledge that exists in the world, and believed that nothing could exist of which we did not know.
A person who peremptorily denies the existence of anything which is beyond the horizon of his understanding because he cannot make it harmonise with his accepted opinions is as credulous as he who believes everything without any discrimination. Either of these persons is not a freethinker, but a slave to the opinions which he has accepted from others, or which he may have formed in the course of his education, and by his special experiences in his (naturally limited) intercourse with the world.
If such persons meet with any extraordinary fact that is beyond their own experience, they often either regard it with awe and wonder, and are ready to accept any wild and improbable theory that may be offered to them in regard to such facts, or they sometimes reject the testimony of credible witnesses, and frequently even that of their own senses. They often do not hesitate to impute the basest motives and the most silly puerilities to honourable persons, and are credulous enough to believe that serious and wise people had taken the trouble to play upon them "practical jokes/' and they are often willing to admit the most absurd theories rather than to use their own common sense.
It seems almost superfluous to make these remarks, as perhaps none of our readers will be willing to be classified into either of these two categories ; but nevertheless the people to whom they may be applied are exceedingly numerous, and by no means to be found only among the ignorant and uneducated. On the contrary, it seems that now, as at the time of the great Paracelsus, the three (dis)graces of dogmatic science self-conceit, credulity, and scepticism go still hand in hand, and that their favourite places of residence are public auditories and the private visiting-rooms of the learned.
It is difficult for the light of truth to penetrate into a mind that is crammed full of opinions of which it tenaciously clings, and only those who accept the opinions of others, not as their guides, but only as their assistants, and are able to rise on the wings of their own unfettered genius into the region of independent thought, may receive the truth. Our modern age is not without such minds.
The world is moving in spirals, and our greatest modern philosophers are nearing a place in their mental orbit where they come again into conjunction with minds like Pythagoras and Plato. Only the ignorant schoolboy believes that he knows a great deal more than Socrates and Aristotle because he may have learned some modern opinions in regard to a few superficial things, or some modern inventions, with which the philosophers of old may not have been acquainted ; but if our modern scientists know more about steam-engines and telegraphs than the ancients did, the latter knew more about the powers that move the world, and about the communication of thought at a distance without the employment of visible means.
If the anatomist of to-day knows more about the details of the anatomy of the physical body than the ancients, the ancients knew more about the attributes and the constitution of that power which organises the physical body, and of which the latter is nothing more than the objective and visible representative. Modern science may be successful in producing external appearances or manifestations with which the ancients were not acquainted ; the initiates into ancient sciences could create internal causes of which modern science knows nothing whatever, and which the latter will have to learn if it desires to progress much further.
The Life and Doctrines of Paracelsus (1887)