Hello Mehmet & welcome to Typophile. Before the members suggest you anything — it would be useful for them to know what is your topic about. Also, Bree is a sans serif font designed particularly for large sizes, it is advised to use serif fonts for long texts; particularly if the content is academic.

If this were an advertising job designed to grab peoples' attention on casual inspection, such charmingly decorative fonts might be just the thing. OTOH, a PhD thesis generally has a captive audience already, and in any case is intended to convince people by virtue of its content, not its typography.

What you want here is something that (a) is comfortably readable, (b) looks professional, and (c) doesn't get in the way of the content. IMO anything else is not only superfluous, but counterproductive.

When typesetting book or academic text – or anything where the content is the critical aspect – the ideal font is one which the reader doesn't even consciously notice, so long as it accomplishes (a), (b) and (c) as noted above. Any 'message' that the fonts convey should be strictly subconscious.

(I've heard more than one professional say that when they see overtly beautiful fonts in resumes or academic work, their immediate thought is "OK, what's the author trying to hide?")

For the body text, I definitely think serif type is called for. (I know some people challenge the theory that serif types are easier to read in running text, but I'm a firm believer in that particular orthodoxy.)

Thanks for the responses. I've been looking for a clean serif font for a while and haven't found one I can settle on.

My thesis is on the natural barrier that exists between the blood and brain (to protect the brain and provide all the nutrients it needs in a carefully controlled way), and uses our current understanding for the design of next generation drugs to treat brain conditions. Not exactly bed time reading!

Since it's a thesis it's not something that people would ordinarily come across, so my font selection is more about reducing reader fatigue and clean presentation, rather than pulling them in for aesthetics.

I've been looking for a clean serif font for a while and haven't found one I can settle on.

my font selection is more about reducing reader fatigue and clean presentation, rather than pulling them in for aesthetics.

Simplified structure (if that's what you mean by "clean") doesn't necessarily correlate to ease/comfort in reading. Personally, I think a traditional face like Bembo, Galliard, or Janson makes for superbly readable, comfortable text.

If by "clean" you're thinking of something more in the transitional vein, I recall seeing an article not long ago which claimed that people were statistically slightly more likely to agree with something set in Baskerville than with other fonts. For a PhD it might be an edge worth thinking about. :-)

If you want something specifically open and uncluttered, Constantia actually isn't a bad face, although I'm not sure how well it would hold up for dense multi-page writing.

Speaking personally, for a long time I favoured Marty Pfeiffer's Nu Serif for prose. It's a nicely neutral serif face which is easy to read, although the high x-height may not be everybody's cup of tea.

I think by clean I mean light. A lot of the Serif fonts I've come across feel very heavily weighted. Text feels really boggy and dark (to me) with anything I've tried except for CMU Serif.

Bembo or Garamond Light might do the trick! I'll have a play and see how they look.

There is a reason for some fonts having a darker texture — as Alex mentions; it makes the printed matter more comfortable to reader. I would go with Garamond, but it will take someone very experienced in typography to make it work well. If you are having trouble in choosing the right font, it's better to pay attention to what will professionals recommend. I would advise you to use either Cambria or Constantia as your main body font.