Ayer claims that human knowledge is of two sorts:(1) Empirical knowledge (like our knowledge of "Snow is white") is based on sense experience. Such knowledge can be more or less probable, but never certain.
These summaries and problems deal with Chapter 4 and 5 of Ayer's Language, Truth and Logic. These materials are copyrighted (c) 1998 by Harry J. Gensler but may be distributed freely.(2) "A priori" knowledge (like our knowledge of "2+2=4" or "All bachelors are single") is based, not on sense experience, but rather on the meaning of terms.