Is this a contradiction in Wikipedia's definition of temperate zone? Under the Wikipedia article Temperate climate Temperate climate in the introduction is describes:


  In geography, the temperate or tepid climates of Earth occur in the
  middle latitudes, which span between the tropics and the polar regions
  of Earth.




So by this sentence I take the temperate zone to be between the pink shaded area (the tropics, and the uppermost and lowermost broken lines (arctic and antarctic circles. This is simple enough.

Then in the next paragraph it says:


  The temperate zones (latitudes from 35° to the polar circles at about
  66.5°, north and south) are where the widest seasonal changes occur, with most climates found in it having somewhat balanced influence from
  both the tropics and the poles.


Now it says that the temperate zones are between latitudes about 35 degrees from the equator to the polar circles. This is different than the earlier description, which said it was between the tropics and the polar circles, which is about +- 23.5 degrees to the polar circles, not 35 degrees.

A little lower it says:


  The north temperate zone extends from (approximately 23.5° north) to
  the Arctic Circle (approximately 66.5° north latitude). The south
  temperate zone extends from (approximately 23.5° south) to the
  Antarctic Circle (at approximately 66.5° south). Zones and
  climates


So now it's saying again the temperate zone is between the tropics (23.5 degrees latitude) to the polar circles.

Lower again it specifies that there is a suptropical zone, namely:


  Subtropical climates are generally located between 23.5° and 35° north
  or south on the eastern or leeward sides of landmasses.
  Humid subtropical climates


It's now specifying zones of the subtropics, but it doesn't change the fact that in the first instance it says the the temperate zone is between the tropics, +/- 23.5 degrees, and the polar circles, and then says the temperate zone is between 35 degrees to the polar circles, a definition which excludes the subtropics from the temperate zone. 

Which one is correct? Is there a contradiction here? If so, is it a mistake or something more subtle I don't understand?
Note that they say:


  the temperate or tepid climates of Earth occur in the middle latitudes


The word in can be used to convey that the first thing is only a part of the larger second thing... much as, for example, Texas is found IN the United States, or the preteen years are found in childhood. 

But by including the additional further explanation of what the middle latitudes are directly after that, I agree it leans a reader towards your interpretation, and is ambiguous and likely confusing to others.

I'll try to make some minor adjustments to the article to hopefully alleviate any confusion.

But in all honesty, it's probably better to not get overly caught up in such excessively precise categorizing.  I tend to believe that what one person, even one climatologist, might call temperate climates may well vary from what another one would classify them.
For example, they can be based on temperature ranges, on prevailing wind patterns, on breaking into equally-sized regions (like Fred commented), etc.

Really, I'd think of the subtropics as sort of a blurry boundary between the tropics and the temperate zone... where the closer you get towards the Equator, the less seasonal variability and frequency of cold air intrusions.

Indeed, even typical places well across into the "official Tropics" can see occasional years with some notable cold fronts, as happened in Cuba and even Costa Rica in the winter of 2010.  So it's not like 23.5 is some magic physical boundary just because that's the northern extent of the sun's latitudinal cycle. 

 

So the Wiki article as you read it appears to be saying the temperate climates are only 35° and 66.5°, only a subsection of the middle latitudes.  But honestly, exactly what you classify the boundaries as is sort of like arguing over which states are in the Midwest or Southern Southern US -- very unnecessary outside of very specific circumstances, and prone to at least occasional dispute probably even among experts.  Yes, a teacher or test may ask you to know their specific definition (whether of temperate boundaries or of which states are in the Midwest)... that's just part of life sometimes.

But the real take-home idea towards understanding how the Earth and specifically climate/weather work is just that there's a Polar region which has very cold polar air basically year-round, a Tropical region which has very warm Tropical air year-round (outside of colder mountains!), and then a "battle ground" that shifts seasonally and even daily in between, altering the weather significantly in those locations.  And local factors like bodies of water and wind regimes can significantly shift regions into a large array of different expected weather