Why do you need to do a postdoc after getting your PhD?
No, it's not like a second PhD, because there's little to no documented requirements, no thesis, no defense, no coursework, etc.
In the 'old days' (prior to the squeeze on academic funding and exponential increase in PhD candidates), one took a post doc primarily to:
- Learn a new skill, technique, or method
- Dedicate a few years time conducting research to strengthen one's CV without the added stress of teaching and other tenure-track requirements.
Ideally, the post doc came out a very desirable candidate armed with a great research program and toolbox.
Today, a post doc is quickly becoming mandatory for academic-track scientists, as the pool of jobs shrink and the pool of candidates expand. It is not uncommon to find people doing multiple post docs, or people finding themselves in a permanent post doc (or research scientist) position.
While this is somewhat discouraging, the simple fact that funding is scarce and science can be expensive suggests that the ideal candidate has a proven track record and is likely to secure additional grants. Post docs provide one the time and resources to prove that tangibly.
Why do you need to do a postdoc after getting your PhD?
In practice? Because very likely you won't be able to get any better (academic) job than that.
These days "postdoc" simply means a research position that is not permanent or indefinite (e.g. tenure track). It is far, far easier to land (yet another) postdoc than a permanent position.
This applies to the fields I'm familiar with (mostly sciences). The humanities may be different.
It's not a second PhD, because the length of the postdoc is typically much shorter than that of a PhD.
The function of a postdoc is sort of an "advanced apprenticeship," where you may choose your advisor (who should be different from your graduate advisor!) according to several possible goals, including:
- Learning a new technique or field
- Gaining further experience in a slightly different area from your graduate research
- Personal needs (such as the "two-body" problem)
Such positions usually last anywhere from one to four years, depending on funding. Your duties will also likely involve helping to supervise some of the graduate or undergraduate students in the group. You may or may not also have some teaching duties. But you typically don't have the obligation to write grants and "bring in" money.