In my university, after passing a viva voce examination, it will take more than 3 months before the university issues an official letter/transcript/certificate to certify that one is officially a PhD holder. Of course, after PhD viva, it will take some time to perform correction as stipulated by examiners. It can be major/minor correction. After a PhD candidate passes viva exam, is she/he unofficially a PhD holder? Considering that one has yet to successfully correct one's thesis as instructed by examiners during viva exam.
At my American university, the process of officially getting a PhD was tiered. It went something like this:
No claim to being a PhD until after successfully defending.
Some informal claim to being a PhD after successfully defending. The committee members would usually make this explicit by congratulating the successful defendee with "Dr.".
A weird quasi-official claim when the university's official degree-completion tracking system formally acknowledged that the student has officially met all degree requirements and is scheduled to receive their degree at graduation.
Official claim upon graduation (whether or not attended).
Verifiable official claim once you have the piece of paper, which may be several weeks after graduation if not attended.
Folks I knew were reluctant to claim PhD-status until graduation, but I think that hiring managers in academia and industry tend to find the caveat of not having been through the ceremony to be fairly trivial. Family and friends are especially unlikely to care about that caveat, except as an excuse to talk about how exciting graduation'll be.
Nobody is going to quibble with you calling yourself a PhD after you've passed your defense, assuming everything went well. For legal purposes such as employment you are not technically a PhD until your university says you are, but in between those times you can honestly say "I've met all the requirements for a PhD and I'm waiting for graduation in the Spring".
It is not uncommon to be asked to make changes to the dissertation, or even do some extra experiments/investigation. Usually committee members consider these to be minor changes that do not require another defense, though they might withhold final approval signatures until they're satisfied. The point is that the committee members themselves do not expect the requested changes to be major endeavors- more of a refinement than substantially new work.
If your committee fails your defense then obviously you're still not a PhD in anybody's view.
Unofficially, YES. Officially, NO.
It is country and university specific. In my university (and in the country where I am working now), it works like this.
The Ph.D. student submits his thesis, checked by his own supervisor(s). This is then checked by the Academic Research Dean.
Once, it passes the above step, it goes to at least two/three external reviewers: one/two examiner(s) in the same country, another examiner in a different country.
The examiners usually get 3-6 months to review the dissertation. Time depends on field and department.
The outcome of the review is one of the following, which is decided by academic research dean and few other Ph.D. quality members:
- Accept as it is
- Accept with minor revision (comments from examiners)
- Accept with major revision (it goes again to the examiners, but less time for review is provided)
- Reject (usually unlikely; based on history)
Once the thesis is accepted (either of the first three of the above), the examiner(s) comes to the students' university for viva-voice. This process is called the `defense'.
Mostly, since the dissertation has been formally accepted if the student defends the thesis in front of the examiners and the Ph.D. panel, he is congratulated at the end. From this, he can assume himself to be graduated.
The official transcript and degree take some time to be conferred on him. Until the official transcript is received, one should not assume to be "officially" graduated.