Shoe

Intensional: A material object, made by people, designed to fit over the human foot; relatively more rigid than a "sock"; made for any of a variety of protective or decorative purposes.

Extensional: A hiking boot; a women's high-heeled shoe; a canvas sneaker; a Birkenstock sandal; a men's dress shoe; a cowboy boot; a geta.

Hope

Intensional: An emotion, felt by human beings, associated with contemplating a pleasant possible future, while not contemplating possible failings of that future.

Extensional: No idea ...

Wire

Intensional: A material object, made of metal, very much longer than it is wide or thick; usually circular in cross section. Produced in bulk by drawing, not stamping or casting. Sometimes insulated with plastic or other electrically non-conductive materials for purposes of electrical transmission.

Extensional: A strand from a Cat-5 cable; a power cord; a lead from an electronics kit; a strand of electric fencing; the cutting edge of certain kitchen tools such as egg cutters or cheese slicers.

Green

Intensional: A color of thus-and-such frequencies.

Extensional: The leaves of various deciduous trees in spring; grass; a pea pod; the light emitted by particular LEDs or laser diodes; simulations of grass such as AstroTurf; a highway sign; certain military uniforms; certain parrots, lizards, or fish; water populated by certain species of algae.

Politician

Intensional: A person whose economic or social status depends on representing some constituency in a legislature, elective office, or other office of government.

Extensional: Cicero; Metternich; Jefferson; Huey Long; Jerry Brown; Rick Santorum.

Apple

Intensional: The fruit of various trees of genus Malus; having a size to easily fit in the human hand; frequently roughly spheroid in shape; sweet or tart in flavor; green, yellow, or red in color; possessing a fivefold symmetry readily observable in cross-section; easily distinguishable from the quinces of genus Cydonia by not being fuzzy or starchy; and from the pears of genus Pyrus by shape and by not being granular in the texture of the flesh.

Extensional: A Granny Smith; a Golden Delicious; a Red Delicious; a Pink Lady; a McIntosh; a Jonathan; and a few crab-apples of various sorts.

Easiest to hardest: Shoe, wire, apple, green, politician, hope.

Shoe

Intensional: Article of clothing primarily designed to be worn on the foot.

Extensional: Hiking boots, flip-flops, snowshoes, Vibrams.

Hope

Intensional: Human sensation of the anticipation that a severe negative outcome will be avoided, when the circumstances are outside of one's control.

Extensional: A student waiting to receive the result of their final exams, for which a passing grade is required to pass the course. A rationalist wishing that cryonics will be successful. A religious person praying to God to cure a family member's cancer.

N.B. Perhaps it is useful to distinguish between hope and optimism. We may want to call a person who constantly looks at the positive effects of a situation optimistic; it seems more appropriate to use "hope" when the stakes are higher and there is an element of desperation.

Wire

Intensional: Piece of material designed to efficiently carry electrons (low-cost and relatively high sensitivity to changes in electric potential across distances) across its length.

Extensional: CAT-5 cables, power lines, circuit board wiring.

N.B. The efficient criteria implies the thinness and longness of the wire, relative to the wire capacity.

Green

Intensional:

1. A certain wavelength of light, the intensity of which directly corresponds to the signal strength of the human M-type cone when such light is shone upon it.

2. The attribute of an object that directly corresponds with the reflectivity of the aforementioned wavelength of light shone upon it.

Extensional:

1. Output of a green laser, the green spectral line of Mercury, the output of a light filter that only lets green light through.

2. The reflectivity of green paint, the reflectivity of grass.

Politician

Intensional: Person who is popularly known for having had a significant direct impact on politics (the policy and/or decision-making part of a government or otherwise a large, self-sufficient group of people with shared interests) and has done so for a significant amount of time.

Extensional: Chuck Schumer, Schwarzenegger, Gandhi, Deng Xiaoping

Apple

Intensional: (taken from Wikipedia, since I can't come up with anything better and I don't know much about taxonomy) The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family (Rosaceae).

Extensional: McIntosh apple, Granny Smith apple, Red Delicious apple.

N.B. For almost everything, including apples and genera, it is often more useful to think about whether something is more blegg-like than rube-like, than to think about whether an item is a blegg or a rube.

Difficulty of generating intensional definition (easiest to hardest): Shoe, Wire, Hope, Green, Politician, Apple

I found it very easy to generate extensional definitions once the intensional definitions were generated. However, this may have been a side effect -- once I came up with examples that fit my intuition, but did not fit the intensional definition, I would revise the intensional definition to include it.

I found it easier to generate definitions when there's a clearly defined purpose for the entity in question. It's harder to define things when there are seemingly arbitrary boundaries (in the case of apple and politician).

For purposes of this post, I choose a single definition for each word and use it in both sections.

Intensional Definitions

1. Shoe: A piece of clothing enclosing and protecting the foot, designed to be worn while walking.

2. Hope: Confidence that a favorable outcome may be reached in circumstances when good rational reasons exist to expect an unfavorable one.

3. Wire: A long, thin piece of drawn metal.

4. Green: Light that tends to activate gamma cones in human eyes more strongly than beta or rho cones, where gamma cones have a peak wavelength of 534-555 nm, beta 420-440 nm, and rho 564-580 nm.

5. Politician: An individual who negotiates policy decisions in a decision-making body by making promises and agreements with those who have influence over that group.

6. Apple: An approximately fist-sized fruit with a thin peel, whose flesh has a crisp mouthfeel and tart flavor, and whose flesh tends to turn brown when exposed to air.

Order of subjective difficulty (least to most): wire, green, hope, shoe, apple, politician.

Extensional/Ostensive Definitions

1. Shoe: The most common type of object pictured in a Google search on the term 'shoe'.

2. Hope: The emotion opposing that of despair in people who find themselves in dire straits.

3. Wire: The stuff used to make coathangers, and the conductive part of electrical cables.

4. Green: The reflective color of chlorophyll, Granny Smith apples, and unripe oranges; the emissive color of the flame when doing flame tests of molybdenum oxides and sulfides, barium carbonates and sulfates, thallium, and antimony.

5. Politician: Most people who run for public office in the United States.

6. Apple: The fruit traditionally used to represent the fruit of the tree of knowledge of good and evil in the Biblical story of the Garden of Eden.

Order of subjective difficulty (least to most): wire, green, apple, politician, shoe, hope.