The “counterfactual” is a mood or inflection of language that signals a departure from reality and an entry into the realm of hypothesis — instead of speaking about what is we speak about what might be or non-real statements.
The Chinese counterfactual is quite an specific topic in Chinese grammar, thus information (or, rather, clear information for language learners) about it is hard to find online.
This article about the Chinese counterfactual and the comparisons between the Chinese and English counterfactual is written as an opinion by me, based on personal research and empirical language experience. I have also read a book about it and several smaller articles. References are listed below. This article contains a lot of explanation of these concepts which may initially be hard to grasp (it may just sound like a bunch of “theory”), so at the end I am going to attempt to give as many great examples as possible to illustrate all of the principles spoken of and refer back to them.
Please note I have had several PHD / academics reach out to me about this article over time, some of their comments are below. I do not have formal credentials to write on this subject, just real-life language learning for many years. I think what this article brings to the table over more academic treatments of the subject is simplicity and an explanation that is easy to understand and good examples of real-life language scenarios.
Let’s start with the English counterfactual, and “subjunctive” for analogy and reference
The “subjunctive” is a grammatical mood or inflection wherein we express counterfactual arguments and thought. The subjunctive can also be used in English (and other Indo-European languages) to express certain emotions like longing / wishing, and other things like necessity, desire, purpose, and suggestion.  However the focus of this article comparing the English and Chinese subjunctive is on the counterfactual element of the subjunctive — in other words, the departure from reality.
The subjunctive in English is typically characterised by the inflection of verbs. Inflection in a linguistic sense means a change in the form of a word to indicate a change of its grammatical function. A simple example would be the change from “Specify” to “Specified” which changes the function from the present tense to the past tense. An understanding of this concept of inflection is very important when entering a discussion about the Chinese counterfactual and its distinction with the English counterfactual.
In English, when we wish to express a counterfactual argument or hypothetical situation, we use the subjunctive to clearly mark our departure from normal “factual” speech into the realm of “what if” or “possibilities” (called an “irrealis mood”). It is this structure that allows counterfactual argument in English to be easier and more naturally identified.
Finally before we go over some examples, I want to mention the opposite of the subjunctive, which is the indicative, (called a “realis mood” — or a mood or inflection which indicates things that are real and true) this is important to mention in this discussion because as we will see later on the difference of Chinese is an absence of a very clear distinction between the indicative and the subjunctive (even though counterfactual argument is possible in Chinese)
Examples of the counterfactual English subjunctive in daily conversation
There are actually several types of subjunctive in English as mentioned before, but this article is focused on the counterfactual. Here are some examples:
“I wish you had come to my party” — note the past tense of the word “have” (had), note that when you say this sentence it implies that the listener did not come.
“If I were you, I would not pursue dancing as a career” — note the past tense of the verb “to be” (were) and the past tense of the word “will” (would)
“Babies need to change orientation in the womb in the final few weeks, otherwise their feet would be facing out first instead of their head” — note the past tense of the verb “to be” (would) as an indication that this is a counterfactual statement.
Now that the picture of the English subjunctive (as a reference point) is clear, let’s turn to the Chinese subjunctive.
The Chinese subjunctive
Let’s start with an overall statement about the Chinese subjunctive, and then explicate it with a few paragraphs, and then give several examples.
Counterfactual sentences are definitely possible in Chinese, but they are not expressed in the way we usually refer to as the “subjunctive” because In Chinese there are no verb inflections, hence when departing from “reality” to “counterfactual” the distinction is not as transparent as in English (and other languages), and consequently all counterfactual sentences expressed in Chinese are in the indicative mood, I.E they are grammatically similar to their non-counterfactual counterparts…
However, in Chinese there are unique markers (individual words) that are often used to indicate a departure from reality into counterfactual, one specific one, 的话, (Dehuà) is frequently associated with a departure from reality into the counterfactual (but not always). Hence counterfactual sentences in Chinese are not as natural and the distinction between the so called “irrealis mood” and the “realis mood” is not as transparent as in other languages. This is the main message and opinion of this article.
Some Chinese “subjunctive” sentences don’t involve any of these markers either, and these will be illustrated later in the examples.
The function of “如果。。。就” (Rúguǒ. . . Jiù) in both “subjunctive” and “indicative” in Chinese.
“如果” (Rúguǒ) is translated to “if” in English. 就 (Jiù) is often translated (when used together with “如果” (Rúguǒ) in a pair) to “then” in English, in English the words “if … then” are associated both with indicative (realis mood) and subjunctive (irrealis mood), for example, “if it rains today, we will not be going to the beach” (realis, indicative) and “If it rained today, we wouldn’t have gone to the beach” (irrealis, subjunctive, notice that this implies that we did go to the beach).
Note that the function of 就 (Jiù) in this situation can sometimes be replaced by other similar words like 并 (bìng) or 才 (Cái) depending on the inflection of the sentence.
In Chinese this is the same, the structure “如果。。。就” (Rúguǒ. . . Jiù) is used for both realis (factual / indicative) and irrealis (counterfactual / subjunctive) moods. Again we will illustrate this through many examples at the end of this article.
“的话” (De huà) sometimes saves the day for the “Chinese subjunctive”
This particular word, “的话” (De huà), I believe is the answer we are looking for with regards to the Chinese subjunctive. Actually “的话” (De huà) has many uses and implementations in Chinese, so it is not exclusively associated with counterfactual sentences, however, I have found that most sentences that most closely resemble the subjunctive in English involve the use of “的话” (De huà), however, couterfactual sentences also can be expressed without “的话” (De huà). Later on in this article I will translate those original English sentences into Chinese and some of those translations will involve the addition of “的话” (De huà)
In case all of that was just boring, here are some solid examples to illustrate the above
Here are some examples to illustrate the principles and ideas discussed above:
Example #1: “I wish you had come to my party” — 我希望你有来我的聚会 (Wǒ xīwàng nǐ yǒu lái wǒ de jùhuì)
–I believe this is a good subjunctive translation as this Chinese sentence does imply that you did not come to my party. Notice that this neither has “if, then” nor “如果。。。就” (Rúguǒ. . . Jiù), nor does it have “的话” (De huà), yet it is still a counterfactural sentence, speaking of something after the event. This could be thought of as like “Chinese past tense subjunctive”
Example #2: “If I were you, I would not pursue dancing as a career” — 如果我是你的话, 我并不会把舞蹈作为我的职业 (Rúguǒ wǒ shì nǐ dehuà, wǒ bìng bú huì bǎ wǔdǎo zuòwéi wǒ de zhíyè)
— this is a great example of a counterfactual sentence in Chinese that conforms to a similar structure very often used English counterfactual (if I were you…), please note that in this instance I have chosen to use the word 并 (bìng) to accompany 如果 (Rúguǒ) for inflection purposes, but I could have easily substituted it for 就 (Jiù) or 才 (Cái) This sentence illustrates the power of 的话 (de huà) in adding a subjunctive inflection.
Example #3: “Babies need to change orientation in the womb in the final few weeks of gestation, otherwise their feet would be facing out first instead of their head” — 在怀孕的最后几周里, 宝宝需要在子宫里转换体位, 否则的话, 他们就会脚先出来而不是头先出来 (Zài huáiyùn de zuìhòu jǐ zhōu lǐ, bǎobǎo xūyào zài zǐgōng lǐ zhuǎnhuàn tǐwèi, fǒuzé dehuà, tāmen jiù huì jiǎo xiān chūlái ér bùshì tóu xiān chūlái)
— This is another solid example of the subjunctive in Chinese, I chose this sentence because the first part of the sentence (babies … gestation) is not subjunctive but merely a statement of necessity, and then the conjunctive adverb “otherwise” is used to switch the mood of the sentence into a subjunctive / counterfactural one, which is reinforced by the presence of “would”. in Chinese, 否则的话 (fǒuzé de huà) plays exactly the same role in switching the mood or inflection of the sentence into a counterfactual one, note the presence of “的话” (de huà), and later on you can also see another marker “就” (jiù) present as well.
Example #4: (This example was actually a Chinese sentence in the first instance, I am going to translate it back to English)
In a Chinese TV show called 非诚勿扰 (Fēichéngwùrǎo) female guests to the show get to interact with male contestants to see if they are interested in potentially dating in the future, in this episode, a girl danced with a guy on stage. This particular dance opened a discussion with the rest of the female guests in the show. After one of them spoke, the host said the following:
“你在想象一下， 刚才跳舞的人不是17号, 是你, 你会怎样？”Nǐ zài xiǎngxiàng yīxià, gāngcái tiàowǔ de rén bùshì 17 hào, shì nǐ, nǐ huì zěnyàng?” 
My English translation: “Just imagine this again, the girl who just danced were not number 17 but were you, what would you do?” —
This English translation feels a little weird without the “if”, but it’s true to the original since the Chinese sentence did not contain a “如果” (Rúguǒ). This sentence is clearly a “subjunctive” / counterfactural sentence because the event spoken of (the dance that had just occured) was not with the girl this comment is addressed to.
I will be adding further examples of the Chinese subjunctive later on as I encounter or think of them but I think the ones present here are very clear and appropriate.
This article will change over time as I can refine it, come back later if you are really interested!
To your Mandarin Chinese learning success!
References and scholarly discussion
 The linguistic shaping of thought, Alfred Bloom. I have actually read this book but disagree with his findings to an extent (I partially agree and partially disagree), my opinion/position is clarified in the this article. In summary: I found his English – Chinese translations lacking and thus his test methodology flawed. Chinese does have a semblance of the subjunctive but it is not as clearly defined as in English, but counterfactual thought and speech is certainly possible in Chinese (as per exampes given in this article)
Furthermore several other scholars have disagreed with some of his findings as well: for example
a) Language in Society, On the linguistic shaping of thought: Another response to Alfred Bloom, Donna Lardiere
b) Pictures of Ghosts: A Critique of Alfred Bloom’s The Linguistic Shaping of Thought, P. Wenjie Cheng
 Subjunctive Mood, Wikipedia, http://en.wikipedia.org/wiki/Subjunctive_mood
 非诚勿扰 Some episode, forgot when!