Right Brain/Left Brain vs. Conscious/Subconscious
Many pop psychologists divide mental work into "right brain" and "left brain" functioning. The right brain is supposed to be the holistic, intuitive, creative, emotional side. The left brain is supposed to be the logical, analytical, verbal side.
This division was inspired by interesting research with "split brain" patients, that is, patients who had had brain surgery which cut the connection between the two hemispheres. The research showed that the left hemisphere specializes in language and analysis, and the right hemisphere in less verbal activity. But serious scientists concur that pop psychologists distort the findings of neuroscience. There is no absolute localization on the two sides. In many cases, one side can develop needed connections if the other side is damaged.
The right-brain, left-brain division became popular because it is a metaphor for emotion vs. reason. Those who discuss "right brain/left brain" encourage you to use both sides of your brain, i.e., both reason and emotion.
I agree with this advice as far as it goes. You cannot be a successful thinker by ignoring your emotions, and you cannot be a successful creator by ignoring logic. However, I don't think the advice is particularly powerful, because it doesn't provide any guidance for how to direct the parts of your mind to work together.
A much more powerful way to divide up mental functioning is the division I learned from Ayn Rand: conscious vs. subconscious.
Your conscious mind is your present frame of awareness. Within this frame of awareness, you can attend to a handful of objects or ideas. You can attend to objects in the world, and to feelings in your body. You can also attend to ideas provided by your subconscious.
But the total number of units you can discriminate at any one time is small: 3ish, 5ish, or 7ish, depending on how you count it. And what you attend to is under your volitional control.
In contrast, your subconscious is your mental database of past observations and conclusions. It stores your memories, values, and vocabulary in a connected form, presumably in the brain.
The subconscious starts out "tabula rasa." You have no memories or knowledge or even values when you are born. You start only with your senses, and some basic physical needs which are tied into the pleasure/pain mechanism.
Once you become aware of objects in the world, and you start experiencing pleasure and pain, these observations and experiences are stored in the subconscious, thereby forming your values and your memories. The information in the subconscious database is built up gradually, through experience. Once language is learned, it grows more quickly, and becomes organized, by means of one's own concepts and conclusions, and the concepts and conclusions learned from others.
As an adult, there is a vast amount of information in your subconscious, most of which you are not aware of at any given time. I call it information, because it may or may not be true: erroneous conclusions can be stored, and formerly true conclusions can become out of date. The information does not correct itself.
Specific information gets triggered in response to objects or ideas in conscious awareness. Whatever you are aware of in your conscious mind triggers related stored information. This stored information then comes into awareness with different intensities, similar to loudness and softness. If an idea is closely related, it will be "loud." If it is more tangentially related, it will be "soft."
Since you can only attend to a few different objects at once with your conscious mind, you may "hear" only the "loud" ideas triggered from the subconscious, unless you take special steps to attend to the "soft" ones.
One causal implication of this view is that all thoughts and feelings come from the same subconscious database. The differences between thoughts and feelings are only:
a) How closely related is an idea is to your values? The closer to values, the stronger the feelings that will be generated by it.
b) Were the connections made by a conscious analysis or by an association? The consciously-made connections will be easier to put into words, and therefore easier to identify.
Unlike the right brain/left brain distinction, this conscious/ subconscious distinction leads directly to practical advice. For example:
1. Any idea that occurs to you, whether you label it as a thought or a feeling, comes from the same source: your subconscious databanks. Therefore, all such ideas, whether thoughts or feelings, need validation. "Should's" may or may not be true. "Want's" may or may not bring you pleasure.
2. Because there is much more information in your subconscious than you can possibly attend to at once, you need techniques to help you systematically draw out relevant information at a rate you can handle it. Tools such as "thinking on paper" help you to do this.
3. If you don't take control over your attention, you will run by whatever "loud" thoughts come up from your subconscious. The passive approach leads you to be driven by rules, habits, and emotions.