- You can study Psychology at Cambridge through either the Psychological and Behavioural Sciences (PBS) course or the Natural Sciences (NatSci) course. Both PBS and NatSci will allow you to graduate with a British Psychological Society accredited degree. This is the first step to becoming a chartered Psychologist, such as a: clinical, educational or neuro psychologist. However the accreditation is contingent on your choosing the right papers (this is more of an issue in the natural sciences tripos).
- Both courses offer the benefits of the Cambridge supervision system. This is where you will meet with academics to discuss an essay/assignment in groups ranging from 1-5, depending on the paper.
Typically, degrees at Cambridge allow you to start with breadth, and then specialise into what your really interested in. Indeed, this has led to the confusion about the (old) "Politics, Psychology & Sociology" tripos and "NatSci" tripos and where psychology fits in (see below). Whether you decide to apply for the Psychological and Behavioural Sciences Tripos or the Natural Sciences Tripos, Cambridge will give you the opportunity to study many different different subjects in your first and second year, other than psychology. This is not something to be feared- it will make your degree stand out amongst the masses of psychology graduates in the UK, and introduce you to fascinating subjects you barely knew existed! In addition, because of the fast pace of Cambridge, "you'll have achieved the same standard and depth in your final year as graduates from more specialised courses elsewhere" Cambridge University Admissions.
Historically, the lack of a standalone "Psychology" course at Cambridge has made it difficult for prospective students to discover how to study psychology at Cambridge, with most psychology graduates coming from the Natural Science (or "NatSci") tripos, and secondly from the (old) Politics, Psychology & Sociology (PPS) Tripos. The introduction of a Psychological and Behavioural Sciences (PBS) course, open for admissions from 2013, whilst the PPS tripos changes to the HSPS tripos and no longer offers psychology routes in the second year.
Note: the new Human, Social & Political Sciences (HSPS)  tripos contains the psychology introduction paper but does not contain second & third year psychology routes.
Psychology through the Psychological and Behavioural Sciences Tripos
Why study psychology through the BPS tripos?
- Lack the science A Levels for Natural Sciences? PBS has no required A Levels- most papers offered do not require specific A Levels- even the biological anthropology paper does not require biology A Level (for example).
- Psychology is featured more strongly throughout your degree.
- A broader scope of psychology is taught (see below)
One difference between the two courses is in the optional papers one can take. If you want to take optional papers in chemistry, physics, physiology, ecology, biology of cells, etc., then natural sciences may be up your street. Some of the optional papers are shared between the two courses, such as "evolution and behaviour", but PBS undergraduates may also take subjects like: biological anthropology, social anthropology, archaeology, sociology, international relations, and so on. One should note that for natural science "evolution and behaviour" is the only paper looking at behaviour in the natural science course for the first year.
Course structure of PBS
You take 4 papers in total: the 2 core psychology papers in section A, and 2 out of the additional papers in section B.
Since the first two PBS papers will be shiny-new, there is little infomation available on the precise content of them. There will be practical elements to the Research Methods paper and BAN 1 (biological anthropology) has "practicals" (although these are unmarked and consist of passing round skulls around a lecture room- fun!). (Source: PBS Course Structure)
Years 2 and 3 are more focused on psychology than first year.
You take one paper in social psychology, and either an experimental psychology paper with a research project and an additional paper, or a biological and cognitive psychology paper and two additional papers. (Both experimental psychology and biological and cognitive psychology involve laboratory experiments.)
You write a research dissertation, and can choose three other papers from experimental psychology, development and psychopathology, and other topics offered each year.
(Source: Cambridge University Reporter)
Admissions information for PBS
It is not required to have a detailed knowledge of psychology. Everything is taught assuming no prior knowledge.
For PBS 366 applications were made for 65 places in 2012
Compare to Experimental Psychology at Oxford: 270 applications for 50 places
The likelihood in 2010 of getting in was slightly higher at Oxford EP (18.5%) compared to PPS (17.6%), but natural sciences at Cambridge took the lead with 26.8% chance of getting in. However the difference is so slight that the course content and the city (Oxford having a larger city centre, and Cambridge being prettier) should have a greater impact in deciding on which university to apply to.
Psychology through the Natural Sciences Tripos
The first year of Natural Sciences contains no Psychology papers, although there is some Psychology content in the Evolution & Behaviour paper (mainly animal studies). Second year is when you can start studying Psychology as its own paper, alongside two other papers. Experimental Psychology in second year doesn't have any compulsory first year choices, however you may find it useful to take at least one essay-based option. The compulsory first year Maths papers provide a good background for the statistical side of Psychology.
In third year (part II), there are a number of options that include Psychology: Psychology, Cognitive Neuroscience, BBS Psychology, and Physiology & Psychology. The first is the only course that is accredited with the British Psychological Society (allowing you to go on to further Psychology training without doing a conversion course), however there are benefits of doing one of the other three courses if you do not wish to go into a career as a psychologist. For example, the BBS option allows you to study a minor subject, such as Psychology of Education or The Human Animal, alongside your major subject of Psychology.
Because of the high science content of this pathway into Psychology, it requires at least two Science subjects at A Level, including Maths and Further Maths, and excluding Psychology. Most applicants have at least three Science subjects. The typical offer is A*AA, although this may vary based on your background and the college you apply to.
Which one to go for?
The first question to ask yourself is "have you got the A Levels?". For PBS, there are no required A Levels, though you will find mathematics, sciences, and humanities all useful preparation.
For Natural Sciences however you will need chemistry to take biological papers, whilst biology is useful but not essential. "It is highly unlikely that you will be admitted to any College without 2 A Levels chosen from Biology, Chemistry, Mathematics and Physics. Most students who apply have three of these subjects to A2 Level."
To see what A Levels are needed for the different paper choices you want to make, go here.