Near the beginning of this work, we are asked to imagine a builder and an assistant who can only communicate with the words "block," "pillar," "slab," and "beam."  
A group of essays on "themes" from this book is collected in Crispin Wright's Rails to Infinity.  Near the beginning of this work, we are asked to imagine a builder and an assistant who can only communicate with the words "block," "pillar," "slab," and "beam."  The work opens with a passage from Augustine which provides an example of "ostensive definition," and introduces the metaphor of "family resemblances" and the concept of a "language game."  FTP, name this unfinished 1953 work which argues against the notion of a "private language," a work which contradicts much of the author's earlier Tractatus Logico-Philosophicus.
A group of essays on "themes" from this book is collected in Crispin Wright's Rails to Infinity.  
Philosophical Investigations or Philosophische Untersuchungen