Talking Heads, The Language Instinct, Steven Pinker

This post is a summary of the chapter "Talking Heads" from the book "The Language Instinct" written by the eminent linguist Steven Pinker. The previous chapter in the book was a discussion on syntax. This chapter focuses more on semantics and pragmatics.

Parse trees are different from parsing.  Parse trees define the syntax or structure of sentences in a language. The process of parsing defines the processing of a sentences and thus is related to cognition and semantics of a language. Chomsky demonstrated this feature of language processing using the classic example "colorless green ideas sleep furiously". This sentence is syntactically right. However it is rife with absurdity and does not make sense at all. In other words, the sentence is semantically not right.

The chapter then discusses the differences between a human being and a machine and how they interpret a natural language sentence. There are various types of sentences: (1) onion (or Russian doll) sentences, (2) garden-path sentences, and (3) ambiguous sentences.

The first two types are hard for human beings because humans are not good at memory as compared to machines. By memory, we mean short-term memory, something similar to a stack for a machine. On the other hand, the last type is easy for human beings because humans are good at decision-making.  The decision making employs different kinds of knowledge such as background knowledge, commonsense knowledge and world knowledge. A classic example that demonstrates commonsense reasoning is given below:

             Woman: I'm leaving you.             Man: Who is he?

The converse is true for machines. Machines can process onion sentences and garden-path sentences because of the availability of memory. However they perform very badly when it comes to ambiguous sentences. In addition to this, machines are too meticulous in parsing a sentences and identifies interpretations that a human being will never detect (e.g. pigs in a pen). 

In real-life, the task of text processing is worsened by the fact that dialogues are filled with short utterances, lots of pronouns, and fillers such as 'uh' and 'hmm'.

The chapter concludes with a discussion on pragmatics. Parsing a sentence involves more than simply understanding the sentence syntactically. A conversation between two parties can either be co-operational or adversarial. In co-operational conversation, the assumptions made by the speaker are also made by the listener. This phenomenon is absent in adversarial conversation. Legal documents demonstrate a form on adversarial conversation by clearly specifying each and every nuances of a contract. The following anecdote demonstrates the difference between the co-operational and adversarial conversation. Two psychoanalysts meet in the morning. The first psychoanalyst greets the other "Good Morning." The other wonders what he really meant by that statement.