Simple propositions are declarative in nature, that is, they make assertions about the condition or nature of a "particular" object of sensation e.g. "This cow is blue", "There's a coyote!" ("That coyote IS "there", behind the rocks."). Thus the simple "primitive" assertions must be about specific objects or specific states of mind. Each must have at least a subject (an immediate object of thought or observation), a verb (in the active voice and present tense preferred), and perhaps an adjective or adverb. "Dog!" probably implies "I see a dog" but should be rejected as too ambiguous.