I have no idea how I managed to write this while my brain was swimming in jello due to brain fog, heat exhaustion and sleep deprivation. But hey I did it. It was getting very long and confusing though so I added divisions.
Their biggest known disagreement is over the Law of 22 Prairial, though surprisingly few people actually talk about it.
[I talk about this in a bit more details here. @anotherhumaninthisworld has a good summary of the situation here too with translated quotes.]
To recap: Gateau writes after Thermidor that Saint-Just actively opposed the law. This could easily be dismissed as Gateau trying to make his friend look better in hindsight (especially since Gateau really bought into the "Robespierre-was-the-sole-tyrant" post-Thermidor kool-aid). But there are very reasonable grounds to support this claim. Specifically, the circumstances around Saint-Just's sudden recall from mission and his almost immediate flight back to the Army of the North - skipping even the Feast of the Supreme Being.
Historically, Saint-Just was the one who delivered the speeches/reports that laid the groundwork for things like the Law of Prairial: his reports on the revolutionary government, on the police bureau, and on the destruction of the factions. This is how he acquired the reputation of the "Archangel of the Terror" (a title coined much later by Michelet). It was a task he acknowledged and reluctantly accepted:
"I have attacked men no one else would have dared to attack, everything might have made a criminal the one who dared, only I had the duty to deliver this dangerous message, it's the youngest who must die and prove his courage and virtue."
When you consider those factors, it is extremely bizarre that the Law of Prairial ended up being Couthon's legislative work. It seems highly likely the Committee originally wanted Saint-Just to draft and present it, but he refused, leaving Couthon to step in.
2. The Failed Reconciliation of the Committees
Other potential sources of disagreement belong to the realm of assumptions as we can't know for sure, but they also have evidence to support them. One of them concerns the events leading up directly to Thermidor: the (failed) reconciliation attempt of 5 thermidor, which La Terreur et la Vertu goes into.
I don't think we have any insider sources on the events themselves outside of Saint-Just's very own speech on 9 thermidor. The Thermidorians seem oddly silent about this. Possibly because it breaks their entire narrative: if they knew Saint-Just was conspiring with Robespierre or was more despotic than him, why did they charge him with that report? The fact that they chose him specifically when it wasn't his usual style of report is also bizarre to me. Like I wondered once: was it purposefully intended as an insult or as a way to drive him and Robespierre apart?
If that was the case, it did seem to briefly work. This is supported by at least one witness: Jacques-Maurice Duplay, interrogated on 12 nivôse Year III. Though he claims he did not hear about the reconciliation proposal, he answers that "they seemed greatly divided" at the time. Considering he mentions that only when they bring this up, it seems related.
When you look at it from the perspective of a linear timeline, Robespierre's speech of 8 thermidor seems like a direct response, an attack even, on what Saint-Just was planning. After a meeting between the two committees on 5 thermidor, Barère announced their reconciliation on the evening and Saint-Just's report was planned and scheduled already. (And I would need to check the date but I think Barère also gave a speech to that effect to the Convention on 7 thermidor.) That Robespierre would publicly undermine Barère seems very likely - but Saint-Just? The day before his own report?
Now the unfortunate part is we will never truly know what happened between them over this. We only have assumptions and theories based on their speeches and other circumstances/factors.
Which brings us to how this friction plays out on screen. The way La Terreur et la Vertu presents it, Saint-Just didn't know about Robespierre's speech, hadn't read it, and considered it unwise. We can only truly infer the last part from Saint-Just's own speech on 9 thermidor. It's clear that if he had anything already written for his, he scrapped and revised a lot based on the events on the 8 and in the night of the 8 to the 9.
Most people don't think of compromise when they think of Saint-Just, but Vinot explains that he was actually willing to sacrifice a massive amount of his own principles and politics to save the revolutionary government from imploding.
On 4 thermidor (July 22), with Robespierre and Couthon absent, the joint Committees finally set up the last four popular commissions mandated by the Ventôse decrees. Even Lindet ended up signing. But the reconciliation on 5 thermidor came at a high prize, like Vinot says:
The decree on the four popular commissions was not followed by any implementing texts. Maximilien received nothing but a few polite tributes. In return, his young colleague had accepted the partial disarmament of the sections, and had given up on the centralization of the police, the purging of the Convention, and the publicizing of his religious policy. With cold composure, he concealed his bitterness and did not decline the responsibility of writing the report.
Saint-Just did not mention in his later speech of 9 thermidor that to get this compromise, he had signed a decree with Barère, Billaud, and Carnot to remove four companies of sectional gunners loyal to the Robespierrists from Paris. He also apparently agreed to "recognize the policing prerogatives of the Committee of General Security at the expense of the Bureau of Police".
Naturally, this uneasy truce was sabotaged almost immediately. On the evening of 6 thermidor at the Jacobins, Couthon gave a speech that essentially blindsided Saint-Just before Robespierre did on the 8:
On the evening of the 6th, at the Jacobins, Couthon admittedly reaffirmed the unity of the Committees, but—forgetting the promise made by Saint-Just—persisted in wanting to crush "five or six petty human figures whose hands were full of the Republic's wealth and dripping with the blood of the innocents they had sacrificed." He targeted only the corrupt representatives and covered the "national representation" with highly emphasized praise. It was a speech in line with the Robespierrist camp, yet moderate enough not to displease the Plain.
In this context, Robespierre's speech on 8 thermidor doesn't seem so explosive. It was only a matter of time.
3. Was There A Rift Between Saint-Just and Robespierre?
Albert Ollivier, whose biography served as the basis for Saint-Just et la force des choses, is a proponent of the theory that Saint-Just and Robespierre were no longer close. He leans hard into the "growing rift" camp. But it's a bit more complicated than that.
First, it completely ignores that in spite of everything Saint-Just still chose that path on 9 thermidor, the way Marisa Linton eloquently put it.
It seems very likely that he had a way out. Multiple, even. He didn't take any. Maybe the reconciliation report was another way they offered him since he refused to be sent back to the North. The pragmatists of the Committees knew that he was a valuable asset to maintain their own power. When they lost him, they lost their leverage against those who criticized the revolutionary government. His final speech was even used to later indict them.
Saint-Just didn't have to deliver that speech. He could have dropped his defense of Robespierre entirely. He could have chosen to submit his report to the rest of the Committees the way he "promised". But they "withered his heart" on that fateful night from the 8 to the 9.
It's possible he knew that reading his speech wouldn't have changed anything - though keep in mind that this is Lindet's perspective, not Barère's, not Prieur's, and not Carnot's extremely elusive one. Actually, Lindet's perspective offers us insight into Carnot's: "The only remaining question was which party would prevail in the Assembly. The only issue at stake was the reputation of Carnot and Robespierre." The whole "Organizer of Victory" PR branding that narrowly saved his ass? He didn't have that in July 1794 - he didn't until Spring 1795. Keeping Saint-Just alive, who was fresh from the Fleurus victory, could have been extremely useful.
Another problem with Ollivier's interpretation is that he inherits a very specific perspective these three specifically gave him, and the post-WW2 context is shaping his argument a lot. (I could go into that more but this whole post is already getting long. Let's just say the specific historical context he writes in influences his interpretation - that's not rare for historians.)
So because of the Thermidorians, you got the eternal pull on Saint-Just's "characterization": was he Robespierre's devoted disciple (Courtois), or his potential rival (Carnot, Barère, Prieur)? Was he going to topple him because he was so much more awesome?
Let's ignore that those arguments only exist because 1) Barère and Carnot were cucked and 2) Napoléon happened.
"Barère and Carnot were cucked" - plz follow for more incredibly srs historical analysis ✌️
Carnot and Barère couldn't admit a 26yo was their equal in power but their superior in personality. They Vampire Chronicle'd us and erased his role in the organization of the war front. Let's be real, his existence was a huge blow to their ego, so they had to paint him as this dangerous fanatic who was even more despotic than Robespierre.
After Napoléon's coup, every historian has tried to shoehorn Saint-Just into a similar category - even Vinot does it. I'm not immune either, it's an interesting concept to play with creatively, but it doesn't belong to reality. Saint-Just's principles were too strong to choose this path.
An interesting thing to consider is that this idea that Saint-Just was a dangerous rival who was about to topple Robespierre reflects the anxieties Carnot and Barère had over their relationship with him more than the reality of Saint-Just's relationship with Robespierre.
4. Was There An Ideological Clash?
Another thing La Terreur et la Vertu but also Stanisława Przybyszewska's Thermidor suggest is that Robespierre and Saint-Just broke apart over certain political issues. Now Przybyszewska's account is very romanticized, and her sources didn't seem to be the most accurate. She also has her very specific interpretation of these figures, which is why I call anything connected to her works "the Stasiaverse" lol.
On the other hand, La Terreur et la Vertu is very closely grounded in Mathiez and Soboul's school of interpretation. This Saint-Just goes on proto-Marxist tangents that seem a bit too perfectly aligned with the interpretations of those historians. He's basically used by the narrative as the mouthpiece to serve a Marxist critique on Robespierre's actions. They support this with the argument that Saint-Just was more to the left than Robespierre, who tried to appeal to the center to the very end.
There seems to be some validity to this though I can't recall a study that actually did this comparative work. Saint-Just's politics are still very much ignored outside of a few historians. Soboul's Marxist analysis most definitely needs to be revised.
What we can say is that Saint-Just condemned Billaud and Collot to the bitter end, pretty much designating them as "the source of the problems" in his last speech, while only mentioning without naming them directly the issues he had with Barère and Carnot. It's possible Saint-Just saw more utility to the latter two, or at least some way to curb them. Billaud and Collot might have felt more unstable to him, and it's also possible he didn't think they actually represented the left. What I mean is I don't think he saw himself as actually attacking the left of the Committee and siding with its center/right. It's possible he saw himself as the left. But it's also very likely he didn't even conceive politics exactly this way. They didn't really use those terms yet. Even though they invented the left vs right divide, it's not quite part of their vocabulary. They think in terms of moderation, indulgence, exaggeration - which all become counter-revolutionary crimes because to Saint-Just they all have the same goal. Factions aren't valid political options to him: they disturb governance, they mislead the Revolution, and should be crushed. But at the same time this position is not explicitly a "centrist" policy in his eyes: it's how the Republic - and the Revolution - can be saved.
So, to answer the question: yes, Robespierre and Saint-Just absolutely clashed, but it wasn't the dramatic, ideological betrayal or the looming power struggle that movies or self-serving Thermidorian memoirs suggest. (Though personally I feel that the narrative presented by La Terreur et la Vertu, in spite of a few anachronistic hiccups in the socio-political interpretation, is the closest to being an accurate reconstruction.)
While the movies/plays dramatize it to create a good narrative tension, they aren't pulling it out of thin air. There was real friction between them at the end, but it was not because they wanted different worlds. They just disagreed on how to get into the next step. Were they going to stop the Terror? To them, stopping the Terror also meant relinquishing the state apparatus that allowed the punishment of the corrupt representatives who threatened the Republic they wanted. Saint-Just fully understood the limits of the Terror, and that it was being weaponized, misapplied and distorted by representatives he didn't actually have the power to control. He had that power in Alsace and in the North - but not in Paris.
The tragedy of their final days wasn't a betrayal of friendship or a battle of secret rivals. It was the realization that the system they built to save the Revolution had become a trap - and while Robespierre chose to blow it up, Saint-Just chose to go down with the ship.