ידע — to know (a fact)

ידע yadá, “know,” is pa'al, root י־ד־ע. It belongs to the large פ״י group whose initial yod disappears in the future and infinitive, and its final ע adds a second weak-root effect. Lexically, it covers knowledge of a fact, information or a skill—not familiarity with a person or place, where Hebrew normally uses הכיר.

Principal parts

Complete conjugation

Ordinary Modern Hebrew uses תדעו / ידעו for plural groups of all genders. The dedicated feminine future תדענה and imperative דענה are (literary). A separate 2fp past ידעתן remains available in careful speech and writing, although colloquial Hebrew often uses ידעתם for any group.

Why the future ends in a

A typical disappearing-yod verb has a tsere in the prefix and another e-vowel in the stem: יֵשֵׁב yeshév, “he will sit,” and אֵשֵׁב eshév, “I will sit.” ידע starts the same way, but its final radical is guttural ע. Gutturals attract an a-vowel, so the final tsere becomes patach: אֵדַע, תֵּדַע, יֵדַע rather than an invented e-final form.

The ע also explains the visible and audible break in יודע, יודעת, ידעו. House romanization writes that syllable boundary with an apostrophe when another consonant precedes it: yodá'at, yod'ím, yad'ú.

The true imperative is דע / דעי / דעו. It is grammatically real but restricted lexically: bare “know!” is rarely a useful command. It survives especially in דע לך “be aware / just so you know” and דעו לכם addressed to a group. Those expressions can sound pointed, so their force comes from context and intonation.

One spelling, three readings: ידע

Unpointed ידע represents three extremely common words:

The past and future differ only in vowels; the noun also retracts the stress. A time expression or a determiner normally settles the reading: אתמול הוא ידע, מחר הוא ידע, הידע הזה.

The infinitive לדעת belongs to the drop-the-yod family with לשבת, ללכת, לרדת and לצאת. These common forms are not built by merely adding ל־ to the past stem, so learn each citation-form/infinitive pair explicitly.

Facts, questions, skills and topics

ידע accepts several complement shapes, each packaging a different kind of knowledge.

ידע versus הכיר

English know hides a lexical split. ידע is for facts, information and knowing how; הכיר is for familiarity with people, places and works. A person normally takes את after הכיר: אני מכיר אותה. A fact or clause normally belongs to ידע: אני יודע שהיא באה.

The choice is semantic, not a formality: substituting ידע for הכיר makes a person sound like a fact to be possessed, while substituting הכיר for ידע changes propositional knowledge into familiarity.

Fixed conversational frames

Several everyday expressions use either ידע or a close alternative:

• אין לי מושג — “I have no idea,” often stronger and more idiomatic than אני לא יודע.
• עד כמה שאני יודע — “as far as I know,” neutral.
• מי יודע למה — “who knows why.”
• לך תדע — “who knows / go figure,” (informal) and fixed in the masculine imperative form.

Key Takeaways

• Learn יָדַע – יוֹדֵעַ – יֵדַע – לָדַעַת together; the initial yod disappears outside the past and present.
• Final ע changes the normal e-vowel future to אדע, תדע, ידע with final a.
• Bare ידע is past yadá, future yedá, or the noun yéda “knowledge.”
• Use ידע for facts, ש־ clauses, embedded questions and knowing how; use הכיר for people, places and familiarity.
• The true imperative survives mainly in דע לך; לך תדע is a separate fixed informal expression.