7.2.s. Summary
Generalizations will be expressed symbolically using quantifiers, operations that take predicates as input and yield sentences as output. More specifically, we will use two universal quantifiers, both written using the symbol ∀ (for all). The sentences formed using these quantifiers will be called universals. The two quantifiers are the restricted universal quantifier, which applies to a pair of predicates to form a sentence, and the unrestricted universal quantifier, which applies to a single predicate. We will apply quantifiers only to abstracts. Since any pair of abstracts ρ and θ can be written in the form [… x …]x and [--- x ---]x using the same variable, we can abbreviate universal sentences as (∀x:…x…) ---x--- and ∀x ---x---, or more compactly, (∀x: ρx) θx and ∀x θx. These may be put into English notation as Everything
, x, such
that
…x… is
such
that
---x--- and
Everything
, x, is
such
that
---x---. (Here the word thing is used as a dummy restriction that merely provides a hook for the relative clause.) The component expressions …x… and ---x---, the restricting and quantified formulas of the universal, will not ordinarily be sentences in the strict sense because they will contain free occurrences of the variable x.
A restricted universal says that the extension of the first predicate to which it is applied, the restricting predicate, is included in the extension of the second, the quantified predicate—i.e., it says that the second expresses a property that is at least as general as that expressed by the first. The unrestricted quantifier says that the quantified predicate to which it applies is universal, that it is a predicate that expresses a fully general property. An unrestricted universal sentence ∀x θx can be restated as a restricted universal whose domain predicate is universal (e.g., (∀x: x = x) θx), and a restricted universal (∀x: ρx) θx can be restated as an unrestricted universal provided we make the attribute predicate conditional on the domain predicate—i.e., as ∀x (ρx → θx).
An English generalization may be analyzed symbolically by using restricting and quantified predicates that capture its domain and attribute. If its domain consists of all reference values, an unrestricted universal may be used, and we need only capture its attribute. In an affirmative generalization, the predicate expresing the attribute will be the quantified predicate of the English generalization while in a negative generalization it will be the negation of the quantified predicate. A formula applying the restricting predicate can be formed from the class indicator C by using the form x is a C, adding negation if the generalization is complementary. (However, we start with x is a person in the case of everyone and no one.) The phrase all and only is used to express a conjunction of affirmative direct and negative complementary generalizations; but a generalization of this sort can be analyzed also by an unrestricted universal applying to a biconditional predicate because the two generalizations it implies can be expressed using an if-conditional and an only-if-conditional, respectively.
The restricting and quantified formulas of a generalization can have as much logical complexity as an independent sentence, so they will often require further analysis. The structure of the quantified formula will usually be indicated in English in the same way as it would be in a sentence predicating the attribute of an individual term, but the structure of the restricting formula may be less obvious. The complexity of the restricting formula can also derive from the analysis of the form of the generalization itself since it is restricting formulas that express bounds or exceptions. Both bounds and exceptions may be captured by conjoining predications to the restricting formula, with the predication negated in the case of exceptions.