e-bilities is based on the most widely researched and well accepted model of mental abilities.

The Cattell-Horn-Carroll (CHC) model arranges our mental abilities into a hierarchical structure:

• General mental ability or gma is at the top of the hierarchy. It is determined by two key mental abilities - our fluid ability and our crystallized ability.
  
  
• Fluid ability refers to "pure" or untutored thinking that depends largely on working or short-term memory. There is a genetic, neurological basis to our fluid ability, and it tends to decline in later life. This is because our working memory deteriorates as we grow old.
  
  
• Crystallized ability includes what we learn in our time at school, as well as the skills, experience and knowledge we acquire later in life. It increases through to adulthood and then tends to remain constant. It depends on long-term memory, which is less prone to the ageing process.

There is also a range of other broad mental abilities that play a part in our thinking, by contributing to either our fluid or crystallized ability. They include:

• Quantitative knowledge - the ability to solve numerical problems.
  
• Broad visual ability - the capacity to attend to and process visual stimuli.
  
• Cognitive speed - the efficiency and speed of information processing.

Just as people differ in their fluid and crystallized abilities, some are better than others at processing information and solving problems that draw on these other mental abilities.

People also vary in a range of higher order thinking processes known as metacognitive skills, which oversee and regulate our mental processes. This includes the capacity to accurately monitor and judge our metal abilities.

Self monitoring of mental abilities plays a key role in learning and problem solving. It determines the degree to which a person will check their work for errors, as well as when they will seek help and clarification in making decisions.