Why does the Buddha, in the Pali Canon, periodically engage in harsh speech?

The sutta excerpt is a translation. It may sound harsher in English than in Pali. Regardless, what was spoken was truthful speech, namely, the monk "misunderstood" Dhamma and the monk "misrepresented the Buddha" and the monk "undermined his own future" if the monk continued to hold those wrong views.

Also, the monk was repeatedly advised by the other monks his view misrepresented the Buddha's teaching but he would not change his views.

Importantly, unlike today with monks who seek to create the own cults with their own interpretations of Buddha-Dhamma, when the Buddha was alive He maintained a strict purity of his teachings within his monastic community.

Also, monks are subject to strict discipline and communal confession. Even today, if a senior monk commits a serious offense he is demoted temporary to a junior, even novice, status, and must tell all monks, including visiting monks, of his transgression. I think this is better than Catholic priest who engage in pedophilia and the Church covers it up and forgives them.

In summary, in the Buddhist Monastic Sangha, censure & confession occur publicly (communally) and thus what could ordinarily be perceived as "humiliation" often occurs.

In conclusion, those who embrace "political correctness" will struggle to understand Buddhism.

To me the tone of the speech is an example of harsh speech.

You are misreading. You are imagining things. His tone is always of compassion.

If I were to use this kind of speech in my day-to-day life I would consider myself not living up to the standard of Right Speech as per the Noble Eightfold Path. I understand, however, that the Buddha controls his speech masterfully. In that case, how did this sort of speech come to be? There is no clause in 'Right Speech' that allows us to engage in harsh speech for the greater good - for example rebuking a monk harshly. That being said, do not mistake this for casting doubt on the Buddha. I consider him a good example of what everyone should act like and his control of virtue, faculties, and activities is something everyone should strive for.

You are trying to criticize Buddha for using harsh speech. If as a father you scold your son sometimes to put him on the right path then is it harsh speech ?

Also, there are several more examples. I have read through chunks of the Pali Canon and there are other Suttas where the Buddha engages in speech I would again consider a violation of Right Speech (not that I have a perfect record of Right Speech). My question is why? Why not rebuke without harshness and adhere perfectly to gentleness?

Criticizing Buddha is like criticizing Father. Such a criticism will lead you towards doubt and confusion. He is rebuking in the best possible way ,in the best interest of the monk.

Harsh speech follow to Collins dictionary:

Harsh actions or speech are unkind and show no understanding or sympathy.

Wrong speech follow to Sutta. Ma. Mū. Verañjakasuttaṃ:

Would talk roughly, saying insolent words that are sharp and cursing. Words bordering on anger and not conductive to concentration. Would say frivolous, untimely, untruthful words, not in keeping with the Teaching and the discipline.

But the buddha's words is more flexible, beniefical, in Sutta. Ma. Ma. Abhayarājakumārasuttaṃ:

1 In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial (or: not connected with the goal), unendearing & disagreeable to others, he does not say them.

2 In the case of words that the Tathagata knows to be factual, true, unbeneficial, unendearing & disagreeable to others, he does not say them.

3 In the case of words that the Tathagata knows to be factual, true, beneficial, but unendearing & disagreeable to others, he has a sense of the proper time for saying them.

4 In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial, but endearing & agreeable to others, he does not say them.

5 In the case of words that the Tathagata knows to be factual, true, unbeneficial, but endearing & agreeable to others, he does not say them.

6 In the case of words that the Tathagata knows to be factual, true, beneficial, and endearing & agreeable to others, he has a sense of the proper time for saying them. Why is that? Because the Tathagata has sympathy for living beings."

So, when buddha blame Sāgata-bhikkhu in VN Surāpāna-sikkhāpada (and the other bhikkhus in many Vinaya rules [sikkhāpada]), it is not harsh speech, because after that, he became an arahanta.

However, in Devadatta case, nobody could change his vindictiveness, so buddha made devadatta as a cause of statute making instead in Vinaya. Mahāvi (1) Saṅghādisesa Dasamasaṅghādisesaṃ. Also, buddha try to keep Devadatta's students instead of him in Vinaya. Culla (2) Saṅghabhedakkhandhakaṃ, so buddha helped Devadatta by helping his students:

the venerable Sāriputta spoke thus to the Lord: “Devadatta, Lord, having split the Order, is setting out for Gayā Head with as many as five hundred monks.”

“Can there not be for you, Sāriputta and Moggallāna, compassion for these newly ordained monks? Go you along, Sāriputta and Moggallāna, before these monks fall into trouble and distress.”

There is much talk about the divine or third eye and yet not much ever said about the divine ear... typically depicted by pierced and stretched out lobes.

Abuse of both the divine eye and divine ear often occur... they are teachers is really the only divine thing about them; If one becomes inflamed by the divine eye or divine ear then they will fall back off the path of the middle way and once again into the two extremes ...No different than with that of the normal eye and normal ear.

The divine ear; is where hearing is meant to come clear not be used in search of the pleasant as an extreme same as with the eye with the pleasant. Such practices are exactly what is meant by the six-fold eternal suffering and the six-fold eternal bliss. That is the upper and lower limit of the duality world of Samsara...

If one in the practice of the hearers: Theravadin were to grasp with their ear a word or sound as a vehicle? They will hear all of it to the very end of it's range. The same way with the eye, nose, taste, sensation and mind as separate and individual consciousnesses. Attaching to dhamma/dharma when heard is suggested to be set upright on the path, attaching to those thus gone is suggested to be set back upright on the path too the other senses etc. the same ...attaching to the extremes is not suggested as it only leads right back into the six-fold world of samsara being attached to the six sense consciousnesses and their six sense consciousness bases.

The Surangama Sutta clearly points to this; there is another Sutta that points out "Knowing one's range" but I don't know the name of it, that is helpful in regard to the senses and their bases too it doesn't specifically state anything about the senses as they on a whole are simply referred to as "range".

Those that practice A Lot will notice the various Bhumi's arises and passing... some may get disturbed like why is a dog laying on the floor? Why is there a corpse in the bed? Those beings do not know their range... and if they do know their range they are there either as help or hindrance. Typically either hindrance to meditation or some help they can't really provide, or not knowing how they even got there to begin with.

The three marks of existence are important in such a case; Impermanent, Not Self, and Suffering... What they want or expect who cares? They're beings that don't know their range.

MN 58:

In the case of words that the Tathagata knows to be factual, true, beneficial, but unendearing & disagreeable to others, he has a sense of the proper time for saying them.

When is the proper time to say beneficial but unendearing & disagreeable words? It is when not saying them would lead to even worse results! In one Pali Canon sutta, Buddha uses a simile of a surgeon saving a patient wounded by a poisoned arror:

Friend Niganthas, it's as if a man were shot with an arrow thickly smeared with poison. As a result of being shot with the arrow, he would feel fierce, sharp, racking pains. His friends & companions, kinsmen & relatives would provide him with a surgeon. The surgeon would cut around the opening of the wound with a knife. As a result of the surgeon's cutting around the opening of the wound with a knife, the man would feel fierce, sharp, racking pains. The surgeon would probe for the arrow with a probe. As a result of the surgeon's probing for the arrow with a probe, the man would feel fierce, sharp, racking pains. The surgeon would then pull out the arrow. As a result of the surgeon's pulling out the arrow, the man would feel fierce, sharp, racking pains. The surgeon would then apply a burning medicine to the mouth of the wound. As a result of the surgeon's applying a burning medicine to the mouth of the wound, the man would feel fierce, sharp, racking pains. But then at a later time, when the wound had healed and was covered with skin, he would be well & happy, free, master of himself, able to go wherever he liked.

The pain in this simile is obviously dukkha, the arrow (as explained in MN105) is craving, the poison is confusion or ignorance spreading the toxins of desire, obsession, and negativity. And the surgeon is Buddha, helping the student remove that craving and clean out confusion -- even at cost of creating short-term pain. Because if the doctor were to leave the poisoned arrow in the body, not wanting to cause pain for the patient, the patient would suffer even more and eventually die!

The way my (Mahayna) teacher explained this to me, there are two levels to our application of Buddhist rules:

• The basic level, when rules are understood simplistically & literally (which is actually the third fetter, known as "silabbata-paramasa" or attachment to rules as a kind of "cargo-cult").
• The advanced level, when the real purpose behind rules is well-understood. That real purpose is preventing suffering and attaining Peace.

When you get to advanced level you are still in alignment with the literal rules 99% of the time. However sometimes, in the remaining 1%, you end up doing things that go contrary to the letter of a rule - in order to uphold the true "spirit" and achieve the "higher purpose".

For example, there is a bodhisattva vow (=training rule) that goes like this:

Not overpowering those on a perverted path.

If, due to laziness malice, you do not expel, punish or deflate the pride of those who need it, you will incur this down-fall. Some situations may require forceful action to stop harm.

-- this is listed as rule #45 of the 46 secondary bodhisattva vows originally coming from Asanga's Yogacarabhumi Sastra.

There are multiple examples in Tibetan Buddhist folklore (e.g. in 100,000 Songs Of Milarepa) of situations when the protagonist was challenged by a "demonic force" and was required to let go of the attachment to pacifism and use some form of (usually verbal, and sometimes magical) aggression.

There is also a not widely publicized early story (Jataka?) about Buddha and Uruvela Kasyapa, the leader of the fire worshipers that Buddha converts 2nd after his enlightenment, shortly after he enlightens his five original friends. In that story, Buddha and Kasyapa get into a dispute about the nature of Enlightenment and each other's attainment levels, and end up "turning into nagas" (snakes) and "exchanging fire". The argument is finished when Buddha is said to manifest even more fire than Kasyapa, which overpowers "the old naga". To me this sounds like an echo of a rather violent debate that involved some heated arguments and possibly yelling.

All this is to say that the use of aggression in Buddhism seems to be justified in some very rare cases when it is required to subjugate a foolish and/or aggressive opponent of Dharma. A typical real-life case (and I have witnessed one in the presence of my Zen Master), is when the person is foolish enough to not notice Master's silent disapproval of what that student is saying or doing, which leads to Master escalating the disapproval to the point of being harsh.

Finally, in Zen and Vajrayana there is a whole other level of "harsh" (unpleasant, disagreeable) speech with Master embarrassing the student to help let go of the egoistic defenses, see one's attachments, and achieve groundlessness. At that level, it is considered a skillful means serving a higher purpose and therefore justified.

Other than these two scenarios (subjugating foolish and/or aggressive opponents of Dharma and murdering student's ego) I don't think I've ever heard of any other scenarios in Buddhism, when the use of "harsh" (unpleasant, disagreeable) speech was justified and appropriate.

But the main idea here is that our long-term goal is Liberation from Suffering. This goal is more important than tiny bit of extra suffering created in students.

The Pali word for "harsh" may be pharusa. According to the dictionary it's used figuratively, and its meanings include "cruel".

As pointed out in a comment the most important question maybe isn't whether it's "unendearing and disagreeable", but whether it's "beneficial" and "said at the proper time".

So that exception was used in this case by the Tathagata to rebuke the monk. Do you know if this case applies to non-enlightened noble disciples or only to the Tathagatas?

I think the Buddha is famously good and knowing people's mind-states, in order to be able to teach them effectively.

So perhaps sometimes he knew that the speech needed to be reproving (sometimes also called "rebuke" or "admonish") to be beneficial.

See also What is a wrathful Buddha? where there's a comment:

That makes sense to me. The example of pretending to be angry with your kids is a familiar experience.

It might also make a difference what sort of relationship exists (e.g. teacher, or parent).

I say this in the hope of answering the question.

Another consideration (according to this collection of Right Speech doctrines) is:

Do I speak with a kindly heart, or inwardly malicious?

It is harsh because it hurts the other monk. The second sentence is true. If we apply the logic you use to any situation, I can justify most of my harsh speech away, removing the actual need for practicing Right Speech. Furthermore there is no clause in harsh speech to justify abusive speech for the sake of helping other beings

Well it might hurt the monk's pride, or something, if not the monk himself -- or "refute his argument" (if arguing is what they were doing).

It's a fairly extreme example, if you look at the previous paragraph to the one you quoted:

"Is it true, Ari.t.tha, that you have conceived this pernicious view: 'There are things called "obstructions" by the Blessed One. As I understand his teaching those things are not necessarily obstructive for him who pursues them'?" — "Yes, indeed, Lord, I understand the teaching of the Blessed One in this way that those things called 'obstructions' by the Blessed One, are not necessarily obstructive for him who pursues them."

See also footnote 1.

I don't think you should take this example as general advice, that you should go around calling everyone "foolish" and "worthless" and so on.

And I don't think that most people can (or should) "justify most of their harsh speech away". Firstly, I think that most harsh speech comes from anger and hurt, attachment and so on, for example:

3. "He abused me, he ill-treated me, he got the better of me, he stole my belongings;"... the enmity of those harbouring such thoughts cannot be appeased.

Hence the question about whether the speech is "with a kindly heart, or inwardly malicious".

Secondly I think that people often respond better to gentle input.

Here we are still talking about this one bit of harsh speech, thousands of years later!

Also, consider the words you're using. I think "abuse" for example is when you're "mis-using" a relationship. The Buddha has some duty (as a teacher), as well as authority, and even a supernatural ability -- to correct one of his errant monks on a matter of doctrine isn't exactly "abuse" (of their relationship).

Whereas most forms of verbal bullying, that I might imagine in lay or family life, maybe is more abusive.

The answer to this comes in the Kesi Sutta:

As he was sitting there, the Blessed One said to him: "You, Kesi, are a trained man, a trainer of tamable horses. And how do you train a tamable horse?"

"Lord, I train a tamable horse [sometimes] with gentleness, [sometimes] with harshness, [sometimes] with both gentleness & harshness."

"And if a tamable horse doesn't submit either to a mild training or to a harsh training or to a mild & harsh training, Kesi, what do you do?"

"If a tamable horse doesn't submit either to a mild training or to a harsh training or to a mild and harsh training, lord, then I kill it. Why is that? [I think:] 'Don't let this be a disgrace to my lineage of teachers.' But the Blessed One, lord, is the unexcelled trainer of tamable people. How do you train a tamable person?"

"Kesi, I train a tamable person [sometimes] with gentleness, [sometimes] with harshness, [sometimes] with both gentleness & harshness.

"In using gentleness, [I teach:] 'Such is good bodily conduct. Such is the result of good bodily conduct. Such is good verbal conduct. Such is the result of good verbal conduct. Such is good mental conduct. Such is the result of good mental conduct. Such are the devas. Such are human beings.'

"In using harshness, [I teach:] 'Such is bodily misconduct. Such is the result of bodily misconduct. Such is verbal misconduct. Such is the result of verbal misconduct. Such is mental misconduct. Such is the result of mental misconduct. Such is hell. Such is the animal womb. Such the realm of the hungry shades.'

"In using gentleness & harshness, [I teach:] 'Such is good bodily conduct. Such is the result of good bodily conduct. Such is bodily misconduct. Such is the result of bodily misconduct. Such is good verbal conduct. Such is the result of good verbal conduct. Such is verbal misconduct. Such is the result of verbal misconduct. Such is good mental conduct. Such is the result of good mental conduct. Such is mental misconduct. Such is the result of mental misconduct. Such are the devas. Such are human beings. Such is hell. Such is the animal womb. Such the realm of the hungry shades.'"

"And if a tamable person doesn't submit either to a mild training or to a harsh training or to a mild & harsh training, what do you do?"

"If a tamable person doesn't submit either to a mild training or to a harsh training or to a mild & harsh training, then I kill him, Kesi."

"But it's not proper for our Blessed One to take life! And yet the Blessed One just said, 'I kill him, Kesi.'"

"It is true, Kesi, that it's not proper for a Tathagata to take life. But if a tamable person doesn't submit either to a mild training or to a harsh training or to a mild & harsh training, then the Tathagata doesn't regard him as being worth speaking to or admonishing. His knowledgeable fellows in the holy life don't regard him as being worth speaking to or admonishing. This is what it means to be totally destroyed in the Doctrine & Discipline, when the Tathagata doesn't regard one as being worth speaking to or admonishing, and one's knowledgeable fellows in the holy life don't regard one as being worth speaking to or admonishing."