Words in Propositions

To determine whether two sentences assert the same proposition:

1. Use techniques of classification and definition to identify the concepts the words express. Two words express the same concepts if they pick out the same class of things.


Jack is a Christian.
Jack is a Protestant.
Jack is a Baptist.

These three sentences express different propositions because the terms in the predicate are at different levels of abstraction.

2. Ignore differences in connotation. Sometimes, words that express the same concept have different connotations. They convey different images or feelings, elicit different associations in our minds, or express different attitudes.


Mary has a firm command of the subject matter.
Mary has a good comprehension of the subject matter.

These two propositions assert the same proposition. However, the first conveys the image of power and control over the material, whereas the second is more bland and doesn't convey an image at all.

3. Find a literal interpretation of all metaphors. To determine how a given proposition is logically related to others, we have to know exactly what the proposition does and doesn't say. If two people are using metaphorical terms in an argument, we won't know whether they are really talking about the same issue until we formulate their positions in literal terms.


My love is like a red, red rose.
My love is beautiful.

These do not express the same proposition. "Beautiful" is a very abstract word. The point of this metaphor is to convey the particular kind of beauty the woman has: the dark and delicate, regal beauty of a red rose distinct from other kinds of beauty.

Comprehension Questions
1 Do the following two sentences express the same proposition?

Native Americans are the primitive people who lived in America before the advent of the Europeans.
Native Americans are the indigenous people of the Americas.

a) Yes
b) No
2 Do the following two sentences express the same proposition?

Insects are dangerous pests.
Each year, insects cause billions of dollars of crop damage.

a) Yes
b) No
3 Do the following two sentences express the same proposition?

Juliet is the sun.
Juliet is a dark and brooding beauty.

a) Yes
b) No

Propositions and Grammar

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