How to reduce the number of hyphenation?

Some time ago, I wanted to deactivate hyphenation completely (without switching to \raggedright).

I found out that setting \pretolerance=10000 turns off the complete hyphenation mechanism: it tells TeX to not even look for hyphenation positions.

In addition, there is the parameter \hyphenpenalty. For example, \hyphenpenalty=10000 will (probably) also suppress hyphenation.

Naturally, forbidding hyphenation might cause underfull/overfull lines. That's why I added \tolerance=2000 \emergencystretch=10pt. The \tolerance parameter controls how much white space TeX considers to be "acceptable"; and the \emergencystretch configures TeX to use at most 10pt of additional white space per line in order to avoid underfull/overfull lines.

My solution to suppress hyphenation completely was

\pretolerance=10000
\tolerance=2000 
\emergencystretch=10pt

Now, I am aware that you expressed doubts on "tuning complicated parameters". But I encourage you to experiment with \pretolerance and/or \hyphenpenalty in combination with my suggestions for \tolerance and \emergencystretch.

The value 10000 is special in TeX, it means "disable this feature" - it is kind of "black or white". I would expect that any value between 0 and 10000 (exclusive) will "reduce" the number of hyphenations (i.e. a "grayshade").

According to my notes, I stumbled over the details on the mentioned parameters in Knuth, D.: Computers & Typesetting – The TEXbook. AddisonWesley, 1986 on page 96.

In my opinion you only get good results by combining two of the already given answers. I am using the following:

\pretolerance=5000

I want some hyphenation, but when it makes sense, so I am not disabling it completely.

\tolerance=9000

I personally do not mind a little bit of space between words and it turned out, that if the tolerance is too low, words might still go over the margin, because a low tolerance leaves tex no other choice, since the whitespace added if the word was moved to the next line, would be declared as unacceptable.

\emergencystretch=0pt

I don't ever want to write over the margin, so no stretching here.

\righthyphenmin=4
\lefthyphenmin=4

I like to get into the flow of a word while reading it before the hyphenation, so that I might already get an idea of what the complete word is. This is more likely to happen, if there are at least 4 characters before the hyphen. If I can figure out what the word is without looking at the next line, the break does not mean that the flow of reading is interrupted.

Disabling hyphenation entirely frequently creates more problems than it solves. You may want to fiddle with the \lefthyphenmin and \righthyphenmin parameters instead. Their default values in many document classes are 2 and 3, respectively; put differently, the left-hand and right-hand fragments must contain at least 2 and 3 letters. You could reset them, say as follows,

\lefthyphenmin4
\righthyphenmin4

and recompile the document. Only words containing at least 8 characters will now be hyphenated. The success rate (i.e., the reduction in hyphenation frequency) of this approach will depend crucially on the language in use; if its words are generally short, you'll likely see a huge reduction in hyphenations.