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2.1

## University of York

Skip to 0 minutes and 0 seconds Welcome to Week 2 of ‘Logic: the Language of Truth’. Last week, we introduced the key notion of ‘deductive validity’ (‘validity’ for short). We saw how focusing on valid arguements can help us to make a start in giving a systematic and objective account of good reasoning. We also introduced the notion of ‘formal validity’. A formerly valid argument is valid because of its logical structure or shape; its logical form. This week, we’re going to look further at the notion of formal validity. At the end of this course, you will be able to analyse and test different types of formally valid arguments. But first, we’ll need a toolkit.

Skip to 0 minutes and 42 seconds The arguments we’re interested in are valid because of how the sentences in them are made up from ‘sentential clauses’ and ‘sentence connectives’. A sentential clause is part of a sentence which could stand as a sentence in its own right. A sentence connective is an expression which attaches to one or more sentential clauses to make a bigger sentence. Here is a simple example. It’s raining in Manchester and it’s sunny in London Here, “it’s raining in Manchester” and “it’s sunny in London” are sentential clauses. Each could be a whole sentence in its own right and the word ‘and’ is the sentence connective which combines them to make a new sentence. This week we’ll start our investigation of sentence connectives with ‘and’.

Skip to 1 minute and 29 seconds Yep, a whole week on ‘and’. We’ll show you a neat way of specifying the meaning of a sentence connective - a truth table - which we’ll use throughout the rest of the module. This is where formal logic comes in. We’re going to specify a new language; a language of formal logic in which key terms will have precisely defined meanings. Then, we’ll use that language to spell out views about what’s going on or meant to be going on, in arguments expressed in everyday or ‘natural’ language and we’ll also start to explore a really exciting

Skip to 2 minutes and 6 seconds and interesting idea, one that we touched on already: that the message that someone gets across with words and specific sentences can differ from what those words and sentences, taken just in themselves, mean. we’ll see that this distinction between strict word or sentence meaning on the one hand, and what gets called ‘occasion meaning’ or ‘speaker meaning’ on the other, is massively important in getting clear about the meanings of words and their logical powers.

# Welcome to Week 2

In this video, Dr Barry Lee introduces the key themes of this week’s content: logical form involving sentential clauses and sentence connectives; and the relationships between the meanings of the sentences that people use when they communicate with language and the messages that they manage to get across by saying them.