We will describe in greater detail the work of Professor Pepperberg and use some examples of Alex's behavior to show what a parrot is capable of doing. If we generalize about his skills, not only can he produce and comprehend sentences, but he also understands concepts of category, "same/different," absence, quantity, color and size. He can tell whether one object is different from another, and whether there is such an object in the room.

- Alex has learned the names of more than 40 objects: paper, key, nut, wood, wheat, truck, "hide" (rawhide chips), "peg wood" (clothespins), grain, cork, corn, walnut, block, box, "showah" (shower), banana, pasta, gym, cracker, "scraper" (nail file), popcorn, chain, kiwi, shoulder, "rock" (a lava stone beak conditioner), carrot, gravel, cup, citrus, back, chair, chalk, water, nail, grape, grate, treat, cherry, wool, green bean, and "banerry" (apple).

- He has functional use of "no," phrases such as "Come here," "I want-," and "Wanna go-" using appropriate names for objects or locations.

- He has also acquired attributes. He can identify seven colors, "rose" (red), blue, green, yellow, orange, grey, and purple.

- He can name five different shapes as two-, three-, four, five -, or six-cornered objects. He uses "two," "three," "four," "five," and "sih" (six) to distinguish quantities, including groups of unfamiliar items, heterogeneous collections, and sets in which objects are arrayed at random.

- Alex has a limited comprehension of "category." He has learned, for example, not only that "green" is one example of the category "color," but also that for a particularly colored and shaped object, "green" and "three-corner" represent two of its different attributes. Thus he categorizes such objects with respect to either attribute based on our vocal query of "What color?" or "What shape?" Because the same object can be the subject of either a shape or a color question at different times, Alex must be able to change his basis for classification. Such an ability to reclassify is thought to indicate the presence of "abstract aptitude."

- He can request or refuse more than 100 objects, categorize and count them, and combine adjectives with the names. In tests evaluating this skill, he has a success rate of 80%.

- Alex has also learned to answer questions concerning abstract concepts, such as "same" and "different." For example, when shown two objects of the same color, shape or material, he knows which category the objects have in common, or in which category they are different. Or if the objects have no category in common, he is able to answer "none."

- The studies also showed that Alex can give the right answers in regard to nouns, colors, shapes and materials not used in training sessions. For example, he can give the correct answer to the question of "What's the same?" when presented with a green triangular piece of wood and a blue one.

- If a trainer hands Alex something different from what he asked for, Alex usually says "No" and repeats his original request. Moreover, he can correctly say which of two objects is the larger or the smaller. If they're the same size, he answers, "None."

- Given a series of objects of different shapes and colors, Alex can say how many of them are, for example, green triangles or blue squares. Able to sort different bottle tops according to size, he can also combine words to say "I want a green nut" or express wishes in simple sentences such as, "Come here."

- To study the parrot's conceptualization ability, Alex was asked, "What color is object X?" Out of 100 objects of different shapes, colors, and materials, he has a success rate of 81.3% in answering correctly. His correct answers show that he understands all the elements of the question and chooses the right answer by obtaining the required information from objects he is shown.