Hume thought that relations of ideas were knowable a priori. 

Hume thought that relations of ideas were only knowable a posteriori. 

Hume thought that matters of fact could be known with certainty.

Ayer uses the verificationist criterion of meaning to argue that metaphysical claims are meaningless. 

Ayer thinks that a proposition is verifiable only if it is strongly verifiable. 

Ayer agrees with Hume that induction is never rational.

In Language, Truth and Logic, Ayer claims that all philosophical claims are nonsense.

According to Ayer, "The Present King of France is bald" is neither true nor false. 

1. Ayer thinks that Russell's theory of definite descriptions is a metaphysical theory. 

Ayer uses Russell's theory of definite descriptions as an example of the sort of thing philosophers should be doing. 

Traditional Rationalism is defined as the view that there is innate knowledge.

Moderate Empiricists deny that there are a priori truths of any kind. 

Radical Empiricists deny that there is a priori knowledge of any kind. 

According to Ayer, if mathematical truths are known empirically then they would not be necessary. 

Mill held that mathematical truths are known empirically.

Ayer claims that a priori truths are "devoid of factual content" and not "about the world".

According to Ayer, a posteriori truths only express definitions of words.

Ayer believes that there is a property of truth and it is the philosopher's job to describe the nature of that property.

Ayer does not believe that there is any property of truth.

The Correspondence Theory of Truth states that P is true whenever P is accepted as a known fact.

According to Ayer, "Stealing is wrong but I like it" is self-contradictory.

The difference between subjectivism and emotivism is that according to emotivism, ethical judgments are reports of emotion and according to subjectivism they are expressions of emotion.

Ayer thinks that ethical judgments are descriptions of the indefinable non-natural moral properties of actions. 

Ayer thinks that ethical assertions are neither true nor false. 

Ayer thinks that ethical assertions are reports of emotion.

The Argument from Illusion is an attempt to show that we do not directly perceive material things. 

In The Foundations of Empirical Knowledge, Ayer claims that the sense-data theory of perception is best understood as a linguistic thesis. 

According to Ayer, a veridical perception is a perception where the thing perceived does not exist.

Ayer believes that the argument from illusion proves that skepticism is true.

In The Foundations of Empirical Knowledge, Ayer claims that the sense-data theory is a "Matter of Fact" in Hume's sense of that phrase.

Stage 1 of the argument from illusion attempts to show that never perceive material things. 

In The Foundations of Empirical Knowledge, Ayer denies that words like "see" and "perceive" have two different meanings in ordinary English.

In The Foundations of Empirical Knowledge, Ayer concludes that we have no grounds for thinking that a material object can exist unperceived.

In The Foundations of Empirical Knowledge, Ayer claims that have empirical evidence for believing that a material object can exist unperceived. 

In The Foundations of Empirical Knowledge, Ayer claims that we have empirical grounds for believing that sense-data can exist unperceived.

In The Foundations of Empirical Knowledge, Ayer claims that if we set aside cases of linguistic confusion, the judgments we make concerning the qualities and characteristics of sense-data cannot be mistaken.

In The Foundations of Empirical Knowledge, Ayer's response to The Speckled Hen Problem is to you can see stars without seeing any determinate number of stars.  

In The Foundations of Empirical Knowledge, Ayer's response to The Speckled Hen Problem is to say that sense-data can possess unperceivable properties. 

In The Foundations of Empirical Knowledge, Ayer endorses The Causal Theory of perception.

In Chapter 5 of The Foundations of Empirical Knowledge, Ayer endorses and defends "strong phenomenalism"—the view that statements that describe material objects can be translated into statements that only describe sense-data. 

Ayer and Hume both agree that experience has a "representative nature", i.e., it intrinsically points to things beyond itself. 

In The Foundations of Empirical Knowledge, Ayer claims that our idea of a material object can be arrived at only after surveying a wide array of sense-data.

 In The Foundations of Empirical Knowledge, Ayer says that veridical and delusive sense-data can be distinguished by way of their intrinsic qualities. 

Austin agrees with Ayer's claim that the plain man takes himself to perceive only material things. 

Austin and Ayer both agree that while the plain man might think that he doesn't need to justify his beliefs about the existence of things like pens and paper, those beliefs do stand in need of justification.

Austin thinks that the argument from illusion establishes that we only perceive material things. 

Austin thinks that veridical and delusive experiences are never distinguishable. 

1. Austin claims that if veridical and delusive experiences were indistinguishable, it would be reasonable to think that they were the same kind of thing.

Austin claims that what Ayer says about the nature of "empirical facts" shows that deep down he believes that the sense-data theory is true. 

Austin believes Ayer's examples of delusive perception support the idea that the word 'see' has two different meanings.

Austin claims that statements about the existence of "moderate sized specimens of dry goods" can never be conclusively verified. 

Determinism is defined as the view that there is no free will

Libertarianism is defined as the view that all human behavior is performed by free will. 

Compatibilism is defined as the view that some of our behavior is free and the rest of our behavior is determined.

Ayer defends compatibilism. 

According to Ayer, introspection provides good evidence that some of our actions are uncaused. 

According to Ayer, an act cannot be free unless it is uncaused. 

Ayer claims that any true statement of the form "All A's are B's" is a law of nature.

According to Ayer, what makes something a law of nature has to do with powers and forces that objectively exist in the outside world. 

According to Ayer, what makes something a law of nature is the way we treat it.

The "Manifest Image" is the name for the version of reality that contemporary physics offers us.

According to Unger, we can use the sorites of decomposition to demonstrate that no physical objects exist.

Erwin thinks that adopting verificationism is the only way we can avoid being mired in go-nowhere metaphysical disputes.

Quine maintains the view that there is a priori knowledge but only of analytic truths.

Quine thinks that the truths of mathematics and logic are known with absolute certainty and completely immune to revision.