There never comes a point where a theory can be said to be true. The most that one can claim for any theory is that it has shared the successes of all its rivals and that it has passed at least one test which they have failed.
Interpretation
The quote suggests that no theory can be definitively proven true; rather, their validity is based on comparative success and ability to withstand challenges.
A.J. Ayer's quote emphasizes the idea that scientific theories are never conclusively true but are instead measured by their effectiveness against competing theories. A theory's credibility is not a permanent state but a reflection of its ability to succeed in tests where others have failed, highlighting the provisional nature of knowledge in the philosophy of science.
In practice
In a scientific discussion about the nature of theories, this quote illustrates the temporary nature of knowledge.
If 'god' is a metaphysical term, then it cannot be even probable that a god exists. For to say that 'God exists' is to make a metaphysical utterance which cannot be either true or false. And by the same criterion, no sentence which purports to describe the nature of a transcendent god can possess any literal significance.
In other words, the propositions of philosophy are not factual, but linguistic in character - that is, they do not describe the behaviour of physical, or even mental, objects; they express definitions, or the formal consequences of definitions. Accordingly we may say that philosophy is a department of logic. For we will see that the characteristic mark of a purely logical enquiry, is that it is concerned with the formal consequences of our definitions and not with questions of empirical fact.
It is time, therefore, to abandon the superstition that natural science cannot be regarded as logically respectable until philosophers have solved the problem of induction. The problem of induction is, roughly speaking, the problem of finding a way to prove that certain empirical generalizations which are derived from past experience will hold good also in the future.
The ground for taking ignorance to be restrictive of freedom is that it causes people to make choices which they would not have made if they had seen what the realization of their choices involved.
The only possible basis for a sound morality is mutual tolerance and respect: tolerance of one another’s customs and opinions; respect for one another’s rights and feelings; awareness of one another’s needs.
The traditional disputes of philosophers are, for the most part, as unwarranted as they are unfruitful.
Where liberty is, there is my country.
The last few hours were certainly very painful," replied Anne: "but when pain is over, the remembrance of it often becomes a pleasure. One does not love a place the less for having suffered in it, unless it has been all suffering, nothing but suffering-
Way back in the 1970s, I was eating a steak, and I looked down, and for the first time it suddenly looked like flesh to me - like a dead creature. In a flash, I realized that every time I ate any kind of meat, something had been killed for me, and I stopped eating all animals, not just cows and pigs but chickens and fish.
I am not yet born; O fill me with strength against those who would freeze my humanity.
The pleasure of despair. But then, it is in despair that we find the most acute pleasure, especially when we are aware of the hopelessness of the situation... ...everything is a mess in which it is impossible to tell what's what, but that despite this impossibility and deception it still hurts you, and the less you can understand, the more it hurts.
The first thing to realize in meditation is that there is no authority, that the mind must be completely free to examine, to observe, to learn. And so there is no following, no accepting, no obedience.
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