There are two different and distinct ways of understanding the Verification Principle. Namely the Evidence Principle and the Content Principle. The Evidence principle sets forth that a statement has literal significance when there are possible observations which are relevant to the determination of the statements truth or falsity. In contrast the Content Principle sets forth that a statement only has literal significance if its content is purely observational in nature, and that the statement is also formulated in observational language.
Of the two differing interpretations of the Verification principle the Content principle is the far stronger of the two. But it also threatens the significance of many ordinary everyday statements about other minds, physical objects, etc. Restores the bite of the Verification principle in quest to lead to the elimination of metaphysics but this comes at a very heavy cost.
Whether Ayer is working with the Content Principle or the Evidence principle is a contentious issue, despite how he officially formulates the verification principle much of the textual evidence seems to suggest that A.J Ayer is working with the Content Principles opposed to the Evidence principle.
What is the status of the Verification Principle?
The Verification principle sets out that every proposition has to be either an empirical hypothesis or an analytic statement. The problem for the Verification principle is that it doesn't seem to be either verifiable by experiential means or by through an analytic tautology. It looks likely that the Verification principle could be self-falsifying.
As Ayer holds that all philosophical statements must be analytic, so should we consider the Verification principle as analytic statement? Though it doesn't appear to be analytic statement, not all analytic statements need be easy to discover, so it could be possible. But as Ayer defines analytic statements as tautologies, it seems more clear that the Verification principle cannot be justified due to it being analytic.
In the book Logical Positivism, a book featuring a collection of essays edited by A.J Ayer. Ayer contends that the verification should be adopted as a definition of meaning justified because we are satisfied with the sentences it permits to be literally significant. But this doesn't seem to adequate to deal with the problem posed. In fact it merely seems to beg the question.
In Language, Truth and Logic, states that 'as to the validity of the verification principle...a demonstration will be given in the course of this book' (LTL, p,23). This seems to suggest an answer to similar to the one given by Wittgenstein at the end of the Tractatus, where he stated the propositions of the book could only be shown not given. The Tractatus was very influential to the thought of the Vienna Circle and this is certainly a possible way to interpret the Verification Principle.
Another answer provided by Ayer came in the 1934 paper published in Mind, called 'A Demonstration of the Impossibility of Metaphysics'. Here Ayer set out the claim that the Verification Principle is the best fit regarding our intuitions regarding the meaningfulness of sentences. But this seems bizarre as the Verification has extremely counter intuitive consequences.
The Task of Philosophy
The task of philosophy is to provide definitions and clear up confusions surrounding the way we use our language. Though the task of the philosopher is not that of the lexicographer whose job is to provide synonymous definitions. But rather by providing definitions in use. This is done 'by showing how the sentences in which it significantly occurs can be translated into equivalent sentences, which neither contain the definiedum itself nor any of its synoyms' (LTL, p.49)
Here we are not dealing synonymous equivalents but translating sentences into equivalent sentences. This involves a reduction of sentences from material objects into sentences which only refer to sense data. The other role is to define the terms of the science's.