What makes tai chi 'tai chi'?

Slow motion movement, chilled out exercise or dance cannot be considered tai chi. 
Tai chi is more than this.
It adheres to certain parameters, guidelines and rules of practice.

Research could save you time & money

A would-be student should take the time to learn a little more about taijiquan before attending a class.
Do a little research.
The time spent will be worthwhile.
You do not want to waste years of your life learning something useless... 

Finding a class

When a new starter scours the web looking for the Art they are faced with an array of approaches that are all called 'tai chi' but are often quite dissimilar.
In truth, there is often little consensus.
It is important to find out what taijiquan really means.

The real deal?

Although many classes claim to be teaching taijiquan, very few are.
In order for the Art to qualify as taijiquan, it must adhere to the essence of the Art:

1. Move your body in accord with The Tai Chi Classics 
2. Train all 13 areas of study
3. Follow Yang's 10 Essentials
4. Maintain medically-sound body use
5. Functionally apply the Art in a skilful 'taijiquan' way
6. Employ the taijiquan principles at all times
7. Embody the teachings of Taoism
8. 13 movements should be expressed at all times
9. Every movement is a whole-body movement

Providing these criteria are met, you have an immense degree of freedom for personal expression and individual interpretation.

How can I tell?

You can easily gauge the credibility of a taijiquan instructor without challenging them to a fight.
Participate in a number of lessons.
Watch the class carefully, see how well they know their stuff, determine how easily and comfortably they can apply their art.
Look for a thorough and convincing show of skill.

Style?

Style is not important in taijiquan.
What matters is the correct application of the taijiquan principles at all times.
Ultimately, style simply reflects differences of interpretation, preferences and individual emphasis.
It is good that people practice different styles; it adds diversity and variety to the Art.

Self defence applications

Self defence moves do not qualify as taijiquan.
They are simply not enough.
You can learn a few self defence techniques quite easily but this does not make you a martial artist.
A credible taijiquan martial artist should have the same standard of skill expected of any martial art: karate, taekwondo, judo, wing chun, ju jutsu, aikido etc. 

Other approaches

Common approaches to tai chi you may encounter:

1. Tai chi tailored for the over 50's
2. Tai chi as keep fit
3. Tai chi-style exercise
4. Tai chi as performance art
5. Numbered forms (i.e. 24 step)
6. Tai chi as dance
7. Qigong referred to as tai chi (shibashi)
8. Taijiquan offered alongside other martial arts by an instructor who practices a variety of systems
9. Tai chi classes offered by a 'learn from a book' or 'fast track' or 'long distance qualification' so-called instructor
10. Tai chi as an add-on to something else, e.g. Alexander Technique "Let's do a bit of tai chi"

The differences between these approaches are worth some consideration.

It had stopped raining; the roads were clean, and the dust had been washed from the trees. The earth was refreshed, and the frogs were loud in the pond; they were big, and their throats were swollen with pleasure. The grass was sparkling with tiny drops of water, and there was peace in the land after the heavy downpour. The cattle were soaking wet, but during the rain they never took shelter, and now they were contentedly grazing. Some boys were playing in the little stream that the rain had made by the road side; they were naked, and it was good to see their shining bodies and their bright eyes. They were having the time of their life, and how happy they were! Nothing else mattered, and they smiled out of joy as one said something to them, though they didn't understand a word. The sun was coming out and the shadows were deep.

(Krishnamuti)

Meditation in tai chi

The meditation aspect of tai chi training encompasses a wide variety of different approaches, all designed to cultivate presence:

1. Attention
2. Breathing
3. Clarity
4. Concentration
5. Consciousness
6. Detachment
7. Emotional awareness
8. Heightened level of awareness
9. Mindful
10. Mushin
11. Seeing & looking
12. Self-awareness 

Every exercise, form movement and partner drill challenges the student to remain here and now.
By bringing the mind to the immediate moment we aim to become unselfconscious - not thinking, not talking, not emoting.
Just being.

Reading & contemplation

Meditation plays an important role in research and study:

1. Awakening
2. Contemplation
3. Exponential development
4. Insights
5. Krishnamurti's descriptions
6. Mystery
7. Perception
8. Rustic
9. Spiritual
10. Truth
11. Understanding
12. The Way
13. Wisdom
14. Words
15. Zen & tai chi

Wide awake

In order to awaken your mind you simply need to be here and now. 
Nowhere else. 
At any given time, nothing else in the universe matters more than what you are doing right now.
The cars outside, the neighbours, the music, the humming of the computer, the smell of food are all part of the moment, and you are nowhere but here.
It is all happening at once and you are totally immersed in it.

On the red earth in front of the house there were quantities of trumpet-like flowers with golden hearts. They had large, mauve petals and a delicate scent. They would be swept away during the day, but in the darkness of night they covered the red earth. The creeper was strong with serrated leaves which glistened in the morning sun. Some children carelessly trod on the flowers, and a man getting hurriedly into his car never even looked at them. A passer-by picked one, smelt it, and carried it away, to be dropped presently. A woman who must have been a servant came out of the house, picked a flower, and put it in her hair. How beautiful those flowers were, and how quickly they were withering in the sun!

(Krishnamurti)

They were chanting in the temple. It was a clean temple of carved stone, massive and indestructible. There were over thirty priests, naked to the waist; their pronunciation of the Sanskrit was precise and distinct, and they knew the meaning of the chant. The depth and sound of the words made those walls and pillars almost tremble, and instinctively the group that was there became silent. The creation, the beginning of the world was being chanted, and how man was brought forth. The people had closed their eyes, and the chant was producing a pleasant disturbance: nostalgic remembrances of their childhood, thoughts of the progress they had made since those youthful days, the strange effect of Sanskrit words, delight in hearing the chant again. Some were repeating the chant to themselves, and their lips were moving. The atmosphere was getting charged with strong emotions, but the priests went on with the chant and the gods remained silent.

(Krishnamurti)