Aptitude vs. Intelligence

Difference between Interest and Aptitude
  This does not mean that interest and aptitude are one and same thing.
  A person may be interested in a particular activity, job or training but may not have the aptitude for it. In such case, the interest shows in a particular occupation or course of study is often not the result of personal attitude but of some other outside influences or reason such as the wishes of parents, the probability of getting a particular job or stipend or other financial help or the prestige associated with the work.


What is the difference between aptitude and intelligence quotient? Ability:- is concerned with present. It indicated the combination of skills, habits and powers which an individual now has and which enable him to do something.
 Achievement:- Looks to the past. It indicates what has been done.
 Aptitude:- Looks to the future and on the basis of the habits, skills and abilities that an individual now has predicts what he, with training, may become and what success he may have in a given occupation or position

IQ is a measurement of raw intelligence. (There is much critique of IQ measurements, and many questions have been raised as to what exactly is it measuring and what all does it mean. Over the years various techniques have been refined to provide better results.) All said and done, IQ does correlate with the cognitive ability of a person, even if somewhat unidimensionally.
Aptitude is much broader than IQ. When we say that someone has the aptitude for a job, it means that that person has various mental/psychological attributes required for the job, including raw intelligence. Some job may require extreme patience, some other may require communication ability, etc. If you do not have those, you do not have the aptitude for those jobs even if you are very intelligent. I am not clear whether physical ability is included in aptitude; I have read analysis and articles that go both ways but it is hard to be surgeon if you cannot stand on your legs all day long.
(Sunil Gavaskar often talks about "temperament" of a batsman. A classic example of a trait that contributes to having the required aptitude to be a good batsman.)

An aptitude is a component of a competence to do a certain kind of work at a certain level. Outstanding aptitude can be considered "talent". An aptitude may bephysical or mental. Aptitude is inborn potential to do certain kinds of work whether developed or undeveloped. Ability is developed knowledge, understanding, learned or acquired abilities (skills) or attitude. The innate nature of aptitude is in contrast to skills and achievement, which represent knowledge or ability that is gained through learning.^[1]

According to Gladwell (2008)^[2] and Colvin (2008)^[3] often it is difficult to set apart an outstanding performance merely because of talent or simply because of hardtraining. Talented people as a rule show high results immediately in few kinds of activity,^[4] but often only in single direction or genre.^[5][6]
Aptitude and intelligence quotient are related, and in some ways differing views of human mental ability. Unlike the original idea of IQ, aptitude often refers to one of many different characteristics which can be independent of each other, such as aptitude for military flight, air traffic control, or computer programming.^[7] This approach measures a variety of separate skills, similar to the theory of multiple intelligences and Cattell–Horn–Carroll theory and many other modern theories of intelligence. In general, aptitude tests are more likely to be designed and used for career and employment decisions, and intelligence tests are more likely to be used for educational and research purposes. However, there is a great deal of overlap between them, and they often measure the same kinds of abilities. For example, aptitude tests such as the Armed Services Vocational Aptitude Battery measure enough aptitudes that they could also serve as a measure of general intelligence.
A single construct such as mental ability is measured with multiple tests. Often, a person's group of test scores will be highly correlated with each other, which makes a single measure useful in many cases. For example, the U.S. Department of Labor's General Learning Ability is determined by combining Verbal, Numerical and Spatial aptitude scores. However, many individuals have skills that are a lot higher or lower than their overall mental ability level. Aptitude subtests are used intra-individually to determine which tasks that individual is more skilled at performing. This information can be useful for determining which job roles are the best fits for employees or applicants. Often, before more rigorous aptitude tests are used, individuals are screened for a basic level of aptitude through a previously-completed process, such as SAT scores, GRE scores, degrees, or other certifications.