Can Mathematica determine part-of-speech for each word in a text?

After downloading and unpacking the stanford Part-Of-Speech tagger that @PlatoManiac mentioned it is easy to call it with JLink:

$POSTaggerPath = "/some/where/stanford-postagger-2013-11-12/";

<< JLink`
AddToClassPath[$POSTaggerPath];

tagString[str_String] := JavaBlock[
  Module[{tagger},
   LoadJavaClass["edu.stanford.nlp.tagger.maxent.MaxentTagger"];
   tagger = JavaNew[
     "edu.stanford.nlp.tagger.maxent.MaxentTagger", 
     FileNameJoin[{$POSTaggerPath, "models", "english-left3words-distsim.tagger"}]];
   tagger@tagString[str]
   ]]

tagString["$HistoryLength=0 may result in lower memory use by discarding old result"]

(* $_$ HistoryLength_JJ =_JJ 0_CD may_MD result_VB in_IN
   lower_JJR memory_NN use_NN by_IN discarding_VBG old_JJ result_NN  *)

To use the bidirectional tagger I had to increase the java memory:

ReinstallJava[JVMArguments -> "-Xmx500m"]

As long as we're talking about leveraging external resources, one could also use http://www.text-processing.com, which offers natural language processing functions (including POS tagging) as a web service.

According to their documentation, "The public API is for non-commercial purposes, and each method is throttled to 1000 calls per day per IP", but apparently you can pay for higher/commercial use.

Anyway, this is an example of how their POS tagging service could be consumed via Mathematica 9 onwards:

tagSentence[sent_String] :=
 Module[{fetched},
  fetched = 
   URLFetch["http://text-processing.com/api/tag", "Method" -> "POST", 
    "Parameters" -> {"text" -> sent}]; (* URLFetch is present in Mathematica 9+*)  
  StringCases[fetched, 
   word : Except[WhitespaceCharacter] .. ~~ "/" ~~ 
     tag : Except[WhitespaceCharacter] | ")" .. :> {word, tag}]
  ]

Note that the string parsing code above is almost certainly not robust.

tagSentence["He used to play the role of a used-car salesman in a play."]

yields

{{"He", "P"}, {"used", "V"}, {"to", "T"}, {"play", "V"}, {"the",
"D"}, {"role", "N"}, {"of", "I"}, {"a", "D"}, {"used", "V"}, {"-",
":"}, {"car", "N"}, {"salesman", "N"}, {"in", "I"}, {"a", "D"}, {"play", "N"}, {".", "."}}

As of Mathematica 11, the function TextStructure seems to do pretty well. You can add "PartsOfSPeech" as an argument to specify that you just want to see the parts of speech of the sentence. The example the documentation gives is TextStructure["The cat sat on the mat.", "PartsOfSpeech"] which yields