The Non-Essential Predicables of Property (differentiae) and Accident - Ch. 3.7 from "The Reasonable Person" by Mark Grannis

Here are the essentials from ch. 3.7 from Grannis' book 

Property

"...a predicable based on a characteristic that is non-essential but follows necessarily or exclusively from some essential characteristic."

[this would be a quality that is belongs to the entire species or genus (at least potentially).]

Example: Humans have hair. 

Accident

"...any predicable based on a characteristic that is non-essential and does not follow necessarily or exclusively from any essential characteristic." 

[This would be a quality in relation to a particular individual in question.]

Example: Socrates does not have hair. 

Specific Property 

"...if a property follows necessarily or exclusively from a characteristic shared by our species..."

By necessarily is meant - "Q follows necessarily from P if Q must be true whenever P is true." 

By exclusively is meant - "Q follows exclusively from P if Q cannot be true unless P is true."

Generic Property

"If a property follows necessarily or exclusively from a characteristic shared by our genus."

Summary 

"One type of (species) expresses the entire essence; two others (genus and difference) express something essential but not the entire essence; a fourth predicable (property) expresses something non-essential but nearly essential (like our mortality or our ability to speak and laugh), and the fifth predicable (accident) expresses nothing essential and is not particularly closely related to anything essential (like our size relative to a Ford truth)." 

Method

You have to first determine the subject versus the predicate in the sentence. 

Examples

Justice is a virtue. - Genus - because justice is a type of virtue, but virtue does not define justice completely. 

Justice will improve your soul. - Accident - because this is not a genus, definition, or a property of justice, but an accidental effect on another. 

The trial of Socrates was unjust. - Specific Property - because while it does not define the trial, all trials must be just or unjust by their nature. 

Biology is the science of living things. - Species - because it is a definition which fully describes biology.

Biology studies mammals. - Generic Difference - because it is quality of its definition to study but makes a generic distinction. 

Biology is difficult for me. - Accident - because this is not related to the nature of biology but some extrinsic thing. 

Logic is an art. - Genus - because it is essential to its definition but not all of it and it is a larger category. 

A pistol is a weapon - Genus because of the same as above. 

The radiator is hot. - Accident - because that the radiator is hot at this moment is not essential or a category of the things existence. 

Lassie is a dog. - Species - because dog encompasses everything essential that Lassie is. 

Grass is green. - Accident - because the grass is green currently, but doesn't have to be. 

A maple is a tree. - Species - same as above for Lassie. 

An acorn can grow into an oak. - Specific property - 

Smith can learn grammar. - Specific property - 

A horse has four legs. - Generic difference - 

My desk has four legs. - Generic difference - 

A cow is an animal. - Genus

G.K. Chesterton was witty. - Accident 

Winston Churchill took afternoon naps. - Accident

Winston Churchill painted well. - Accident

Untrained monkeys can guess randomly. - Specific property