Many assume that a person signing in French will understand a person signing in English. This is false, and the gap is larger than one might imagine. So what is the difference between LSF and ASL?
These are two distinct languages, as different from each other as French is from German. An LSF signer does not spontaneously understand an ASL signer, and vice versa.
The most surprising fact concerns their history. ASL directly descends from LSF, via Laurent Clerc, a French deaf teacher who went to the United States in 1816 to establish the first school for the deaf.
Two centuries of separation have been enough to create two autonomous languages, while still leaving a lexical kinship visible today.
Three differences structure this gap.
Firstly, the manual alphabet. LSF uses two hands for some letters, while ASL uses one hand for the entire alphabet.
Next, the vocabulary. Despite their kinship, a significant portion of the signs differ completely, and some identical signs have opposite meanings.
Finally, the grammar, each having developed its own rules of order, facial expression, and use of space.
One point needs to be made. There is no universal sign language, just as there is no universal spoken language.
To learn one or the other with video demonstrations, the Anna: Sign Language app available at annasignlanguage.com covers both LSF and ASL.
In this article, we detail each difference.
What is the common origin of LSF and ASL?
The story begins in Paris in the 18th century, and it explains why two languages separated by an ocean retain a visible kinship.
Abbé de l'Épée founded in Paris, in the 1760s, the first public school for deaf children. He did not invent sign language: he observed the one that Parisian deaf people were already using among themselves, and he adopted it as the language of instruction.
This decision changed everything. A language previously transmitted informally became structured, taught, and disseminated.
The Parisian school trained generations of deaf teachers. Among them, Laurent Clerc, himself deaf and a brilliant teacher.
In 1816, American Thomas Hopkins Gallaudet came to Europe seeking a method to educate deaf children. After a disappointing visit to the United Kingdom, where methods were kept secret, he went to Paris.
There he met Clerc and convinced him to accompany him to the United States.
The two men founded in 1817 in Hartford, Connecticut, the first American school for the deaf. Clerc taught French sign language there.
It is there that ASL was born, through a mixture. The LSF brought by Clerc met the local signs already practiced by American deaf communities, notably that of Martha's Vineyard, an island where hereditary deafness was common and where a unique sign language had developed.
From this meeting, a new language was born.
Two centuries later, linguists estimate that a significant portion of ASL vocabulary retains a kinship with LSF. Enough for the origin to remain traceable, too little to allow mutual understanding.
What are the alphabet differences between LSF and ASL?
The manual alphabet, or fingerspelling, is used to spell proper names and words without an established sign. Here is what distinguishes the two systems.
Comparative table of alphabets
| Criterion | LSF | ASL |
|---|---|---|
| Number of hands | One hand, two for some letters | One hand only |
| Hand used | Dominant | Dominant |
| Position | In front of the chest | Near the shoulder or chin |
| Identical letters | Several in common | Several in common |
| Letter J | Different movement | Traced in motion |
| Letter Z | Traced in motion | Traced in motion |
| Common usage | Proper names, borrowings | Proper names, borrowings, acronyms |
| Frequency of use | Moderate | High |
As this table shows, the most visible difference concerns the number of hands. ASL is entirely practiced with one hand, while LSF uses both for some letters.
This peculiarity has a practical consequence. An ASL signer can spell while holding something in the other hand, which LSF does not always allow.
One point deserves to be highlighted, as it creates an illusion of proximity. Several letters are identical or very similar between the two alphabets, a direct legacy of the common origin.
This partial resemblance is misleading. Recognising a few letters does not mean understanding, and a beginner sometimes believes they are following a conversation they do not grasp.
The frequency of use also differs. ASL relies more on fingerspelling, especially for acronyms and borrowings from English, where LSF favours established signs.
What are the vocabulary and grammar differences?
Beyond the alphabet, the two languages diverge on the essentials. Here are the main gaps.
Comparative table of vocabulary and grammar
| Criterion | LSF | ASL |
|---|---|---|
| Shared vocabulary | Partial historical kinship | Partial historical kinship |
| Identical signs | Some, sometimes different meanings | Some, sometimes different meanings |
| Order of signs | Theme then comment | Often subject, verb, object |
| Facial expression | Grammatical, mandatory | Grammatical, mandatory |
| Use of space | Central | Central |
| Time marking | Timeline in front of the body | Timeline in front of the body |
| Classifiers | Present, own forms | Present, own forms |
| Influence of spoken language | Written French | Written English, frequent acronyms |
As this table shows, the two languages share structural principles without sharing their application.
Facial expression illustrates this deceptive proximity well. In both languages, it carries a grammatical value: it marks questions, negation, and intensity. However, the exact configurations differ, and a signer applying their LSF reflexes in ASL will produce misinterpreted statements.
The use of space works similarly. Both languages position people and objects in the space in front of the signer, a mechanism without equivalent in a spoken language. However, usage conventions vary.
The order of signs is the most confusing gap for a learner. LSF favours a structure placing the theme before the comment, where ASL more frequently follows an order close to English.
One point requires particular attention. Some identical signs have different meanings, which creates real misunderstandings between signers of the two languages.
Can you understand ASL if you know LSF?
No, not spontaneously. You will recognise isolated elements, without following a conversation.
The most accurate comparison is that of French and Italian. Two languages from a common root, with a partially similar vocabulary, and a mutual understanding that remains illusory.
What you will actually recognise falls into three categories.
Some inherited signs from the common origin, sufficiently similar to be identified.
Several letters of the alphabet, since the two fingerspelling systems share configurations.
The structural mechanisms, that is, the use of space, the role of facial expression, and the logic of classifiers.
This last point is a real advantage, and it explains why an LSF signer learns ASL faster than a hearing beginner.
You already master the visual modality. Your eye reads movement, your hands produce precise configurations, and you understand that a language can organise meaning in space.
These skills do not transfer between two spoken languages. They transfer entirely here.
What blocks understanding remains, however, the majority.
The vocabulary diverges on a significant portion of the common lexicon. The grammatical structures do not overlap. And false friends exist, with identical signs having different meanings.
A warning deserves to be made. Partial recognition creates an illusion of understanding that is particularly misleading.
You grasp a few signs, reconstruct a plausible meaning, and you are wrong. This phenomenon mainly affects intermediate learners, advanced enough to recognise but not enough to verify.
Remember the principle: the common origin accelerates learning, it does not replace it.
Conclusion: two related but distinct languages
LSF and ASL are two full-fledged languages, as different from each other as French is from German. A signer of one does not spontaneously understand a signer of the other.
Their history, however, explains their kinship. ASL directly descends from LSF, through Laurent Clerc, a French deaf teacher who went to the United States in 1816 with Thomas Hopkins Gallaudet to found the first American school for the deaf.
From the meeting between the language he brought and the local signs already practiced, a new language was born. Two centuries were enough to make it autonomous.
Remember the three main gaps.
Firstly, the alphabet. ASL is entirely practiced with one hand, LSF uses two for some letters. Several configurations remain identical, a legacy of the common origin.
Next, the vocabulary, which diverges on a significant portion of the common lexicon. Some identical signs even have different meanings, creating real misunderstandings.
Finally, the grammar. The two languages share structural principles, namely grammatical facial expression and the use of space, without sharing their application conventions.
On mutual understanding, the answer is clear: you will recognise isolated elements, without following a conversation. And this partial recognition creates an illusion of understanding that is particularly misleading.
A piece of good news to finish. An LSF signer learns ASL much faster than a hearing beginner, because the visual modality is already acquired. Your eye reads movement, your hands produce precise configurations, and you understand that a language can organise meaning in space.
These skills transfer entirely, which never happens between two spoken languages.
